I only use them on games without clearcoated playfields or games that much older than 25+ years of age. Most of the time they are unecessary.

Not really, both options are susceptible to scratching and ball roll slowdown. Both are made of similar family of polyethylene terephthalate materials. The difference is most present protectors are using PETG versus PET (ie Mylar™, a brand name), meaning addition of glycol to the formula for added pliability and reduce the potential for brittleness which can occur with thicker, aged PET or problems when cutting with a CNC router.

So what IS the real perk here? Best explained via example.
Here is a Paragon I put a protector on due to slight insert sinkage (common) and after clear coat drip method I had to do to correct matters. The protector prevents the wear from ever coming back due to ball rolling on insert edges, and only detectable if you are a pinball collector. It may be hard to spot where the edges of the protector are from the photo, which means the protector was cut correctly and with reduced swarf. There was existing mylar rings around the pop bumpers that had no lifting damage. I recommend zooming in to get a better view. Fitting was overall fairly good with some trimming required. Sticky adhesive Mylar is not something you want to be putting on 40 year old, lacquered playfields, as it will eventually create air pocket bubbles on any uneven playfield surface. Attempts at future Mylar removal results in factory playfield coating damage. Natural static adhesion is more than suitable for protectors. The only other complete correct option is a full clear coat of the entire playfield in this particular case, but is a bit overzealous for minor sinkage.

I still don't recommend protectors for any type of modern clear coated playfields or brand new games, especially in home use environments. They don't need them. Also, they don't protect against significant strikes from airballs or the dimpling that accompanies the same impacts.
Paragon PF Large.jpg