I write more than I read, but both, really. If I'm going looking for something specific, I might look for a combination of characters or a crossover, which will be covered by the tags you have to choose, or I could be looking for a flavour like WWI AU or fics about spanking, and the freeform tags give me that. With no freeform tags, you'd not be able to find specified weird little things like that, and with no necessary standard-form tags, you might not be able to find the characters and ratings you're looking for.

I have something of a regimen of things I tag for in the free field, but I've let it slide and just put in whatever seems pertinent and that I remember at the moment. I try to put "art" in all the art posts and word count in all the fics, at least. Of course I'm not being very kind to my readers in the first place, since I post multifannish challenge output in a single "story". It just seemed like too much work to make it a series, especially when it's art. Having a whole "work" for a single piece of art that is consumed at one glance, or a drabble, didn't really seem like a good idea either.