Cutscenes are non-interactive narrations -- scenes where the players shut up and listen to the DM's rambles. By this definition, cutscenes only involve NPCs.
There's two kind of cutscenes -- plot expositions and railroading.
In plot exposition cutscene (PECS), several true NPCs are doing stuff, unbeknowst from the PCs.
In railroading cutscenes, the PCs become NPCs, under the control of the DM, and the players can't affect what happens during the cutscene. Because, if they could, it wouldn't be a cutscene anymore.
Both types annoy me, both as a DM and as a player. It's frustrating to get his PCs torn out of your grasp and puppetted by a DM that will make him do stuff he wouldn't otherwise. It's also upsetting to be fed information about the plot, information that you would not have otherwise.
In fact, there's only two ways I use cutscenes:
PECS if they're, in game, told by something. It could be a scry spell cast by a PC, an ominous dream, a bard retelling a story, or, in a more modern setting, the PCs watching the tape from a security camera.
Railroads are only used for non-crucial stuff, like when the character goes shopping. For example: "You found an alchemist that could sell you healing salves, tanglefoot bags, and potions of spider climb. You bartered to get a cut, and you got one but only after you bought also half a dozen thunderstones, so you spent more than you wanted to anyway." This is also known as glossing over it.