Practical Reasons
We wear clothes...
1. To avoid bodily harm.
This includes protection from bad weather, certain working conditions, perverts gaining easier access, etc., etc. In some cases, hygiene might be an issue, such avoiding contact with venereal disease. Interestingly enough though, bodily harm is often less of an issue than you think. That is, you can often go nude in circumstances that you might otherwise think is harmful when nude.
2. To avoid upsetting or offending another.
In our forced clothing environment, almost everyone learns to see nude bodies as offensive and unacceptable. In general, they usually learn to associate it primarily with sex, perversity, or loose living. They also learn to fear nudity. In a "clothing optional" environment, mere nudity does not offend people because they see nude bodies as healthy, natural or "normal," and thus acceptable.
3. To avoid tempting another to sin in some way.
When you are not used to seeing nude bodies, the mere sight of one might tempt you to lust or sin in some other way. Of course, sensual indulgence is partly a byproduct of character and conditioning, so chances are high that merely putting clothes on does not help. In fact, I believe clothes actually enhance sensual indulgence by creating greater curiosity about the hidden parts, and sometimes by actually highlighting the hidden parts. Think about how we all react to gifts. When you see a gift wrapped in pretty paper, you begin to wonder what might be inside, and you might even be tempted to try to find out. Keep in mind that society considers clothing an enhancement, often considering it "sexy," and that is precisely my point.
As an aside, as with any good thing, some people do misuse nudism/naturism. Some use it for their own perverse desires, using it as a means of indulging in sensuality, and in my opinion, such people are not true representatives of nudism/naturism.
Impractical or Unhealthy Reasons
While we truly have only a handful of practical reasons for wearing clothes, people today wear clothes for many other reasons. In general, in our (high) society, we "dress up." We enjoy decorating our bodies with fine clothes, and name brand clothes, thinking they make us look better or they somehow improve us. We certainly want others to have a good impression of us, and so we wear clothes as a way to influence what others think. After all, haven't you heard? "Clothes makes the man." In a society that prizes appearance, this seems true. Of course, we do often recognize certain people by their attire. For instance, the military, policemen, firemen, doctors, nurses, judges, etc. Each wears attire that allows us all to quickly recognize what they do or who they are. Even bums and prostitutes have certain looks. The truth is, while appearance has some value, it can be deceptive, and when we dress to impress, we deceive not only others but also ourselves.
Still another reason is fear. People wear clothes to hide. They wear clothes to feel more secure. They wear clothes to create a (physical and psychological) barrier between themselves and others. They wear clothes to try to fit in. because acceptance IS a major concern. They wear clothes out of shame, feeling ashamed of their body and the human body in general. They wear clothes because they know how people judge, criticize, and sexualize, and they want to discourage that as much as possible by avoiding nudity. Again, they fear being naked because they fear what others might think, say or do about it. They wear clothes because it dulls the senses, particularly the sense of touch. As I noted above, we know appearance influences a person's impression, so people hide, hoping to give another impression.
I am sure you can think of still more reasons we wear clothes. How many of those reasons are truly practical or healthy? Probably the most impractical and unhealthy reason for wearing clothes is, our consumer-based, industrialized culture forces us to do so. Have you ever wondered why? Have you ever considered that maybe it is about money, power and control? First, the basis of economy is "supply and demand," and when you require clothes, it creates demand, which in turn generates revenue and profit. In other words, it feeds the economy. Second, the basis of government is power and control, and when you require clothes, it forces someone to enforce that requirement, thus giving someone power and control.
When you require clothes, you ultimate create fear -- fear of going nude, fear of the human body or parts of it, fear of being yourself, fear of what others might think, say, or do, namely enforce the law, etc. Think about how Muslims require their women to wear Burqas. Do you think fear and control aren't part of their lives? And yet other cultures are no different really. I mean, the basis for covering oneself is the same, they just don't require as much covering.
The question is, should we live this way? Should we live in fear and with wrong attitudes, or should we live free?
What Is Your Reason?
Whether you dress to impress, dress out of fear, dress because you think nudity is bad or wrong, or whether dress for practical reasons, the question is, why? Whatever your reason, why is that your reason? Why is that reason a good reason? If you are Godly person, does your reason line up with the truth, does it honor the Lord, does it reflect the Lord's attitude about it?
The truth is, while most people argue that clothing is a necessity, unlike eating, drinking, and breathing, others have to teach you to wear clothes. Oftentimes, they use fear and shame to influence you. They even sexualize it. Ultimately, fear, shame and wrong thinking keep people imprisoned in their clothes, never to experience the freedom that their body and mind needs, the benefits that come from going nude regularly. I say, if going nude is so good, why wear clothes? Again, what is your reason?