Most SQL configurations I've seen either have replication/mirroring or they have a full backup once in a while and a differential backup relatively often so backing up the database normally will interrupt the flow of full to differential backups, creating a hole in the middle where your differential backups are unusable.
So what do we do?
Well, that's why "Copy Only" was made.
And for those who like code:
BACKUP DATABASE dbname TO DISK = 'c:\folder\dbname.bak' WITH COPY_ONLY GO