When it comes to the idea of cropping I tend to have an idea in mind already when I compose, so I can tell that certain surroundings are just filler I'll remove later. Maybe to highlight a certain area of the frame that I noticed in particular. Sometimes that is leading lines with wide streets, sometimes it's a specific colour that stands out. Sometimes it's cropping the image to remove the surroundings so that a person's face and thus expressions are what you want the viewer to notice the most.

Cropping is something I rarely do after taking an image, as in without thinking about it beforehand. But either way I don't think you should feel any sort of guilt over it regardless. The whole point of these high megapixel cameras is that you can crop in and maintain high resolution images. ;^)