I never really noticed much difference in play at all with or without mylar. So I never really got why so many people in there restorations were always pulling it when there was no real need too (unless they were clear coating it).
Like I just got a playfield mostly to use as wall art so this next part doesn't really matter. But before I got it I noticed a little wear in places that I knew were high wear areas because they came from the factory with mylar in place there. I thought; wow it must have been played alot. Upon closer inspection I realized there was no mylar in place at all, it had been pulled (the field was even still sticky). All the damage in the area wasn't caused by the ball. But by some previous person pulling the mylar.
The playfield would have been almost pristine without said past owners actions. Now to be fair it could have been causing an issue. But seeing as the old glue is still on the playfield I'm gonna go with the puller didn't really know what they where doing. They could have been attempting to prep it for new clear coat. But it's a diamond plate and still in nice shape so I don't know. It'll at least look nice on the wall.