Several years ago I'd say, yes. Now I'd probably say, no, unless you are in reduced circumstances.
First of all, the clothes which end up in these stores are nearly never new (sometimes they get some new stuff from big retailers, but it doesn't happen very often). Mostly they are well worn out, and you can see it.They generally don't look very nice per definition, unless it's a well-known quality brand whose owner only put it on a couple of times (granted, this happens, too).
Next, of course, I'm aware that they all get washed and disinfected and what not, but have you never noticed that people generally leave some imprint on their surroundings and the things they use? Like, for instance, in some houses you feel sad while in others you will feel happy?
I realise it sounds a bit new-agey, but you have no way to know what sort of person wore this item before and how it could influence you. I would say it's different with the big stuff like furniture, but clothes is something you put on yourself, close to your skin and then have on a couple of days or even longer, if it's something like a cardi, for instance.
2nd hand clothes are usually quite cheap. Herein lies the problem. You aren't on your guard around cheap things, hence you are much more prone to impulse buying than normally. After regularly visiting a thrift store, you can easily end up with lots of stuff you don't really need or like which later goes direction the garbage can anyway, and you waste more money than buying some new item from a regular store.
Also, nowadays you have cheaper retail and markets which sell decent-looking, average quality clothing which is quite affordable, and doesn't look like something out of Granny's closet. I do think it's different when you get stuff from family and friends, especially for kids who are growing very fast so they only wear these donated items like several months or year at most. Grown-ups are a different matter.
That said, I still enjoy visiting thrift stores. I just noticed that of all the clothes I bought there over the years I only kept like 2 things total, all the rest was like a couple of months on average and then out it went, while most of the new things I buy I keep wearing until they start falling apart. There are exceptions, of course, but still...