My (guitar, hohner) trem will still drop the strings off the fretboard, and can raise the tuning up about a 4th. Add lights in a show, over time..something might drift - or, in a jam (as in session) with no keyboards - the bass may drift out and you have to retune. Happy to say, my strings are >15 years old! Dinged and dented, and very bent (fretwear), i refuse to change them only on principle. After all that, i have a piezo tuner, my pedals have tuners, but i much prefer (in a live situation, especially) using a my ears over a machine - an 'on' snaredrum will soon get those beats beating.