Wilsons Sandbox

A couple more questions in search of knowledge. On this list, there has been a lot of talk about gearing changes, primarily by means of changing the front sprockets. I am curious, why the front sprockets? I was brought up to believe that if you wanted taller gearing, you went to a smaller rear sprocket. If you wanted lower gearing, you went to a larger rear sprocket. The "old" school also lead me to believe that one should leave the front sprocket alone unless absolutely necessary. I don't recall the exact reasons why, but it seemed to be general knowledge that the way to go was with rear sprocket changes. Did I miss something? Is there a particular reason many of you are doing front sprocket changes? Just curious. Jim Sherlock