Nah, scanning is useful alright, though some here seem to do it for its own sake. Or as a competitive sport.
Not to be a wise guy, but a little experience goes a long way- when it's slight picture breakup and/or glitches, and finally a dead halt, it's media almost certainly. And a proper scan will show you bad errors at that exact spot on the disc.
It's not too tough to tell when when you have simple compression artifacts. Call them pixelizing, macroblocking, whatever. And then there can be jerkiness from bad telecine, PAL <-> NTSC conversions, bad authoring, computer bogged down with malware and/or bad fragmentation while trying to render a project, etc. On occasion I've had a disc just dirty enough to play glitchy, usually players will refuse outright any such disc. Experience allows you to distinguish one from the other.
Heh, after re-reading what I just wrote, all I can say is welcome to an interesting hobby.