General Question

I have noticed that most tutorials start with cropping the image down to 100x100. I was wondering wouldn't it be better to fix the image completely then shrink it down to 100x100. I wasn't sure why cropping first was a good idea (I do understand sizing the image to be even, such as 300x300 or whatever so when you shrink it, it will be equivalent).

I was wondering if the cropping was to do a better icon, or if it was just a style preference people had.