Perfect Pitch, or Absolute Pitch is the ability to recognize or reproduce musical notes without the benefit of a reference tone. I have frequently encountered the question of whether perfect pitch is required to tune pianos. The answer to this question is a resounding “No”. Piano tuners always use some sort of a reference, whether that be a tuning fork or an electronic tuning device. Instead of listening to the absolute pitch of a note, piano tuners listen to the beat rates between pairs of notes or “intervals”. (Incidentally the ability to recognize intervals is called Relative Pitch.)
That said, as someone who has had perfect pitch from a young age, I believe there are a couple of perks. For example, I can tell within a few seconds how out of tune a piano is and whether a customer’s piano needs a pitch raise or not, without having to refer to an electronic tuner. (In fact, when I have a customer on the phone wondering if they need a pitch raise, I will sometimes ask them to play me a couple of notes over the phone.) Another minor benefit is that I always know which note I am tuning. I recently tuned a piano on which the top few notes had been tuned an entire half-step sharp! The previous tuner had apparently been using an automatic electronic tuning device, and had gotten off by a note without realizing it. (Of course, perfect pitch makes a tuner immune to that kind of mistake, but so does running checks or tuning aurally.) There are, of course, downsides to having perfect pitch as well. I have a really hard time playing pianos that have been allowed to go a half step flat, organs that have been transposed, and harpsichords that are tuned to historic (eg. A=415 instead of A=440) pitch levels.
But to get back to the original question, no perfect pitch is not required to tune pianos, and it doesn’t really help much either. It can, however, be handy at times.