From an operator's perspective:

Completely unnecessary. Even on route. ESPECIALLY for new games. They are built for this. The last games with truly trashed playfields were from the early 80s. Anything from the 90s on is totally fine without a protector.

Caveat: Some older EM and SS machines that had varnished playfields instead of clearcoated ones, and are now destroyed, need a little surgery.

Option one is a new playfield, but those are expensive, and tedious and time consuming to install.

Option two are these protectors, but these should be a last resort, because they are removable, and they do cause issues like ball hangups and can affect general play. The much better version of these are the hardtop overlays, with the art reprinted on them, and adhesive underneath. Because they are anchored down to the playfield, and cover every little bit of the former playfield, they are the superior option. They take a little more finesse to install and are more expensive, and are only available for a few games as of now. But much better.

However, these are all for emergency surgery to save a game. Never as a precaution. If a game plays nice and is in nice condition, you have nothing to worry about. Enjoy your game, you won't ruin it by playing it without the expensive condom. Like others have said before: wax your playfield, and change your balls and you will be fine.

Maybe to the folks who like said things. We have never paid a premium for a game that had a protector on it. But the poll here is split as to their value or lack thereof. Their true value is to someone who worries about these sorts of things. The value lies in giving that type of buyer, collector, operator, etc piece of mind. If someone worries about it, then the money spent to ease their mind should be worth it. There is no real irreversible downside to having one of these on your games. I don't see them as useful, so I don't have them. But to alleviate a more anxious collector, it seems like a small price to pay (relatively)