+P+ ammo is, by definition, loaded to pressures in excess of industry standards. Few gunmakers endorse its use, and when they do, such endorsements are often informal and/or heavy with disclaimers. Many manufacturers will not honor the warranty of a pistol that is damaged while using +P+.
I do not know Glock's official stance on the issue; I've tried answering this question before, but have always come up with confusing and contradictory information, which is probably what led you to post this thread in the first place.
The "correct" answer is to follow the recommendations in the owner's manual, but the manual is not always crystal clear, as illustrated here...
The Ruger P-Series pistols are compatible with all factory ammunition loaded to U.S. Industry Standards, including high-velocity and hollow-point loads, loaded in brass, aluminum, or steel cartridge cases. No 9mm x 19 ammunition manufactured in accordance with NATO, U.S., SAAMI, or CIP standards is known to be beyond the design limits or known not to function in these pistols.
You have to read between the lines to realize that Ruger is NOT endorsing the use of +P+, as it does NOT meet "NATO, U.S., SAAMI, or CIP standards...", but this fact is not immediately obvious unless you know what the standards are!
Shooters are split on this issue; some avoid +P+ outright, some use it sparingly, and others use it all the time and write off the people in the other camps as worrywarts.
Many +P+ threads degenerate into pointless bickering between the first and third groups.
In the interest of full disclosure, I generally avoid +P+, which is admittedly somewhat ironic because several of my 9mm pistols live on a diet that mostly consists of likewise warranty-voiding handloads!