Even if tuning by ear, when you play with a band or especially are recording, it would be very silly to trust your ear alone because recording hours of takes in an expensive recording studio with many other people's time in a slightly out of tune key would be very disrespectful and wasteful.
Most musicians can tune "relatively" okay, but do not have the ability to tune "absolutely" (perfect pitch).
Here is an example of perfect/absolute pitch that very few musicians have. This is the skill one would need to be able to not use a tuner at all > https://www.youtube.com/watch?v=dw3-k9 (Jimmy Kimmel Puts Charlie Puth’s Perfect Pitch to the Test).
For sure. We always tuned by plugging into tuners when I played in a band. You might get it to closer than completely out of tune by ear, but when you're in close quarters and there's people talking or playing their music, you just plug in and get to the green light.
Most musicians can tune "relatively" okay, but do not have the ability to tune "absolutely" (perfect pitch).
Here is an example of perfect/absolute pitch that very few musicians have. This is the skill one would need to be able to not use a tuner at all > https://www.youtube.com/watch?v=dw3-k9 (Jimmy Kimmel Puts Charlie Puth’s Perfect Pitch to the Test).