We all do at times.. hahaha
neither did I intend to start a brand war with my comment. Just wanted to clear some misconceptions =) and it seems like the others who commented are not Sony users.. Haha.. Sorry for the OT..
I would say the most useful purpose for your flash is that it allows you to shoot at a smaller aperture and faster shutter speed than the ambient light would have otherwise allowed.. Not sure if I'm right. (pros, pls correct me if I'm wrong so that I can learn at the same time)
I found some articles online on flash, perhaps you could start by reading them?
http://www.digital-photography-school.com/an-introduction-to-external-flash-units
http://www.digital-photography-school.com/introduction-to-external-flash-units-part-2
(source: DPS)
http://www.picturecorrect.com/tips/when-you-need-an-external-flash-in-photography/
(source: picturecorrect.com)
http://www.youtube.com/watch?v=i1jRsTPK10Q&feature=youtube_gdata_player
(YouTube)
Note: I do not own any of the websites, articles and video, nor have I contributed to them in anyway, or own the copyrights.
As for prime lens, like area0404 pointed out, it's mind activated zoom. Once your brain detects the lack or excess focal length, it will automatically activate your legs to zoom in or out =)
Hope this helps =)