Aside from possible leaks into the finished ceiling below, these are exactly the reasons I caulked it last time, including the shims.

From a service perspective, I've been the lucky guy to financially prosper from horned wax rings or those new fluidmaster waxless adaptors that jar loose during install, and leak.If the seal doesn’t compress enough to let the weight of the toilet rest on the floor, you’ll end up with a wobbly toilet that puts too much weight on the flange. I used to use wax gaskets all the time till I ran into leaks because the drain pipe was moving a bit and the toilet flange was not secured to the floor properly because there is no floor under the flange. The material’s flexibility compensates for imperfect placement of the toilet while still forming a perfect seal.

This type of gasket will allow you to set the toilet multiple times, unlike wax rings that get smashed once and need to be replaced. I've heard some of those waxless work but I go with what works for me and from the guidelines of liability. I leave the back 10-15% of the base uncaulked (what you can't see at a casual glance), but every toilet I've ever removed has never been water-tight around the flange at the floor, IE; if the seal is leaking the water will drain down around the waste pipe to wherever, not sit under the toilet. The o-ring not only prevents water from coming back but also sewer gas smells from coming back up into the bathroom. My flange is too high and crooked and it's cast iron, either I try that or cut it outIf your flange is to high, and crooked, wax is your friend, as it will seal, and ooze to the side as needed, more on the high side, and less on the low side, but still making a seal.I ended up just using the wax ring that came with the American Standard Champion 4 that I bought today. All this and much more is available to you absolutely free when you register; for an account, so join our community today today! Perhaps if we were lucky enough to wait 39 years after it was initially done it would have been easy, but that wasn't the case here.