BMW's standard saddles are rather had and you will notice that during a long ride. By replacing the saddle you provide more comfort. For people with short or long legs, the standard saddle can also be considered uncomfortable, fortunately for these people we have some great lowered and raised saddles.
Do your back, neck, shoulders or knees get sore easily while riding? Then a combination of a new saddle and handlebar risers is a great option. This will create a much more ergonomic riding position.