I'm like a lot of folks that are most interested in how much they see on their "local patch" (though my "local patch" changes pretty frequently with my work). Seeing 90+% of the birds in your area requires a good understanding of habitat, habits, sounds, and migrations and this requirement to learn these things are what make us grow as birders.
However, I also enjoy travelling to see other places / cultures / and most importantly to me, birds. I also think this helps us to better understand bird families and puts some perspectives on our local birds. While I'm from the Southern US, I have recently moved to Canada, so this summer was the first time I got to see a lot of Warblers on their breeding grounds. Boy, was their behavior, song and plumage different to what I had seen in Florida!