I have never used Incremental backup but I kind of remember reading somewhere about it as a new addition to SQL 2005 when it first came out. I never went back to dig into it as I care much less about this new backup feature as I was not going to use it anytime soon but it was somewhere in the back of my head that it is there if I happen to need it in future.

I read somewhere on online posting, long time ago that Incremental Backup backs up database since the last full backup and the last incremental backup whereas Differential Backup backs up database since the last full backup.