I don't automatically do "one in, one out" but I don't generally let things accumulate too long either. I have the opposite problem -- I let them go too quickly.

I was under the impression ‘discard’ meant to trash, we all interpret it differently. In that case donating, yes I often do buy and donate clothing I feel I won’t wear or what doesn’t fit me, usually the same kind of clothing I just bought so as not to overload my closet with too many of the same top, pants, etc.. the only thing I never have too much of is accessories.

No one-in-one-out for me. Way too strict and literal for the way I shop and live. I generally do a review and purge when I do my seasonal closet switch. I also have kids who are outgrowing stuff constantly so there is always a donation bag at my house. I have a small home and fairly small closet, but I'm not buying a lot of clothes right now, only really to fill wardrobe holes, so things are well under control.
I am running out of room for footwear, so I may have to start thinking about those purchases in a one-in-one-out way, rather than "collecting" things I like as they come along. The goal being not to discard more but buy less. Thanks for the thought exercise.

My approach is similar to Jenn's. I do two major edits per year (at seasonal changes) and do have a donate bag for items I don't plan to keep. I keep some items for many years and others wear out within a season...it all depends.

I’m with Kari and Janet. No specific 1-in, 1-out plan, but I do have limited space/hangers so I need to assess if something has earned its place in the closet.

The only time I’m strict about 1-in 1-out is when I’m specifically buying a replacement. If I’m not, I can easily end up with multiples because I wasn’t quite ready to give up the original. (Yes,I know it makes no sense, but I’m good at rationalizing that the original still had a few more wears, so should stay longer....)

I go through my clothes twice a year when I switch summer and winter items. I weed out stuff that doesn't fit, is worn out, or I don't think I'll ever wear again. My closet tends to stay around the same number of items even without being strict about 1 in -1 out.

I only discard when I purchase if I've found a new item to explicitly replace an old one (either because something is on its last legs, or I find an item that suits me better than a similar one I already had--if it's the latter, I make sure the old one gets to a good second home, which usually ends up being my fiancee because we wear the same size tops and jackets and that's what gets changed out the most). I don't do it as I go as any kind of rule. I don't have a cap for how much I'm willing to own at once other than "Welp, I can't physically fit anything new in here without my closet becoming overcrowded."