I've never used the AE lock button, but my understanding is that I would use it when I wanted to meter on a different subject than I was shooting. (take meter reading, enable AE lock, recompose, shoot). Correct? My question is, isn't is just easier to use exposure compensation for this? When would I want or need to use AE lock as opposed to dialing in the appropriate exposure compensation? It just seems easier to me to preview a photo on the LCD and then just hit the exposure comp dial if I need another shot, instead of dealing with metering and AE lock for another shot.