"All the world is not, of course, a stage, but the crucial ways in which it isn't are not easy to specify." - Erving Goffman
You need one. I don't care if you work in your basement. I don't care if you're an artist. A grown-up man needs at least one suit for special events. And once you have one, a good one which fits you and doesn't make you feel constricted, you will wonder why all your clothes aren't suits. You will want to buy three more.
The standard men's uniform of well-fitting jacket and trousers is a remarkable confidence-giving garment: people will treat you differently when you are in a suit; they will look at you differently, they will ask your opinion, they will expect you to take care of trouble.
To take this one step further, every man should own a custom suit. The first time I purchased a custom suit I knew I would never buy an off-the-peg, ready-to-wear suit from my local department store again. And I haven't. This is one of those things you just won't understand or fully appreciate until you do it. So you'll have to take my word for it until you, too, take the plunge. The way a suit cut for my own measurements - 20 or more - makes me feel is a remarkable thing. The process results in a garment that breeds confidence. I own some very nice off-the-rack suits. A few of them major name brands. But they don't compare. How can they when they only consider 3 measurements? You've got to try it to know what I'm talking about.