I check my rear view and side view mirrors about every 10 seconds. I always know what is around me. If there is someone tailgating me, yes, I'll use my turn signals. If I'm in a busy 4 way stop intersection, yes, I'll used my turn signals. If I'm on a highway merging with lots of traffic, yes I'll use my turn signals. I use them anywhere I believe it's possible to be blamed for a problem if I didn't use them.
On the other hand, if it is 4AM and I'm changing lanes on an empty highway, I will not use my turn signals. Etc. Etc. I am inherently lazy, so to lift my arm to use them if not absolutely necessary is too much work. Must conserve energy for more important things.