You do not have to crop every photo!
Cropping all of your photos will remove a lot of the history from your scrapbooks. When you crop every photo down to a small shape, you may be able to fit more on a page, but you also lose a lot of your life's memories.
This is true of recent pictures as well as your heritage pictures. Pictures you take now will be old someday, and one of the purposes of putting them in the scrapbook is so that your future generations will have a big slice of heritage pie to enjoy! If you crop out all the places of your youth, how will your children be able to describe "how things used to be" to their children?
Read more on taking photos to preserve your "location" history.
Another reason not to crop down your pictures to a very small size is the aesthetic (or artistic) application. We all want our pages to be easy on the eyes! Lots of small objects arranged all over the page just does not please the eye as well as a few larger objects arranged in an orderly way.
Most of the time when a person begins to scrapbook, their first instinct is to crop everything. Sometimes cutting the person totally out of the photo and placing it on your page works aesthetically. But generally, cropping around the tops of heads is not very pleasing to the eye.
There is nothing wrong with cropping your photos, but it is not necessary to crop them all. You end up with a much more eye-pleasing layout when you crop very little.
I rarely ever crop my photos into shapes. They are typically always rectangle or square!

