I TRY to because if my house ever burns down- I will otherwise have a hard time explaining to the insurance company exactly what I had and what condition it was in.
Also- I sometimes forget what I have- so I try to keep current pictures of various collections so I don't double-collect something.
As sort of a side effect though- I've collected and been collected by other people that take pictures of their dolls and toys. Lots of people take artistic pics and I really enjoy seeing what they post.
If you were worried about people taking your photos- you could always screen them to private so that only you can see them.