Can't say I quite know as I've been simply avoiding games with DRM for some time now—unless they're basically given away.
I have read that it can get in the way of fan made mods and patches, which is something of a staple of PC gaming culture (fans "improving" and adding to games they like) [EDIT: this could also mess with game preservation, if the source code gets lost]. I have also heard some claim that it creates an overhead which might slow down a game (reduced fps and the like), though judging by how many people use it without complaints it would seem the effect is maginal at best/worst.
Other than that, I don't know. To me, the worst aspect of DRM (unless it installs some kind of maleware style bullshit on your computer) is that it allows publishers to nerf the game after you have purchased it. For instance, they removed songs from some GTA games, and removed the console in Two Worlds 2 in order to introduce a microtransation store which provided the player with similar services (but now for money). Of course the publishers might still do so on GOG, but at least here I can have an old copy stored away on a hard drive.
Post edited August 30, 2017 by MightyPinecone