It's the nature of the sign business that you have to police customer provided artwork, even art files sent in from other people with actual graphic design jobs. Unless the designer has actually worked in the sign industry before (or had plenty of experience exchanging art files with sign companies) he/she will not think at all about making the artwork friendly to vinyl cutters or routing tables.
Lettering or objects with extra inline/outline paths from the line stroke, outline or path offset effect is just one of the things you have to watch-dog. I don't mind it so much if an outline or path offset effect is "expanded." At least I can hit Ctrl-Y and see the extra paths in the outline view. The one that really gets on my nerves is the practice of laying copies of the same object on top of each other, one object with a fill and the other with an outline effect. The result of this is you may have 2 exact copies of the same source object sitting directly on top of each other. That won't be easy to see unless you're really looking out for it. But the vinyl cutter will sure cut those duplicate objects and even cut clean through the material to do so. There's a lot of "old school" Illustrator users that do this, even though the Path Offset command can do the same thing without all the extra object garbage.
Imported PDF artwork has all of these problems and adds more. Depending on how the PDF was created the file may have all kinds of clipping masks and clipping groups. Some of that stuff will create even more duplicate objects, ones that have no fill or outline stroke. The objects are invisible, but they're still there and a vinyl cutter or routing table will cut them. Astute Graphics' Vector First Aid will delete most (if not all) of these kinds of paths when cleaning up artwork.
Some applications are pretty shifty when creating EPS or AI files. I've seen CorelDRAW do an annoying thing from time to time where it "simulates" compound paths by slicing them during the export process. The application is not very consistent at how it does this. One exported EPS or AI file might be just fine and then another has every compound path sliced up. You'll see the slices when viewing the artwork in wireframe/outline view, but not everyone double-checks that.