Just because they're going to the gym, a lot of guys wear old T-shirts that look like they've been lying in the closet for 15 years. My workout clothes have to work.
For me, what takes up most of the space in my closet are suits. I wear a lot of suits and jackets. But I think every man needs a black suit at home. You can never go wrong in a black suit. But in terms of style, I think it's about being comfortable in what you wear.