You will find that music is much easier to read when it is written within the staff. Ledger lines are very difficult for most to read, especially if your eyes are not that sharp (this comes from a 63 year old who is having cataract surgery in two weeks). Tuba players, bass trombone players, bassoon players, etc. read the ledger lines, but standard trombone parts are much easier to read. If you are reading scores, however, you will find that the trombones usually play tenor parts, not the low bass parts. Bass guitar players read within the staff, but are actually playing an octave down. Yes, it's cheating, but who cares? At least we can read the parts!