Cutscene

The term 'cutscene' refers to an event or series of events within an IF narrative which, once initiated, unfold without any direct player input. (They may be initiated, or sometimes curtailed, by a direct player action. The precise content of the cutscene may also be influenced by earlier player actions). A cutscene usually occurs within a single textdump, but can also unfold over several turns. Intro text is not considered a cutscene.

A dramatic, non-interactive storytelling interlude (typically displayed outside the game engine), in which the IF author briefly takes control of the narrative in order to relay important developments in the plot. For instance, an IF version of Little Red Riding Hood might usefully begin with a cut-scene in which the little girl leaves her house and gets lost in the wood -- afterall, there wouldn't be much of a story if the interactor decides to stay home.

In a multimedia game, cut-scenes may involve video footage of live actors. Cartoon or computer-generated cut-scenes require the time and talents of animators, storyboard artists, voice actors, visual editors, and so forth. Multimedia is expensive to produce; for this reason, multimedia tends to be more linear than classic text-based IF.

Reasons to Use

To save the effort of implementing the scene. It's a lot easier to have the tank column roll past and disappear immediately than to describe each part of it, to produce realistic responses when the PC tries to interfere, and so on.
To carry out actions which would be natural for the PC but which the player might not guess. Used in this way, cutscenes can be valuable sources of character development, and avoid unfair expectations on the player. Do this too often and you will invoke the wrath of your audience, however.
As a tool to influence the pace of a game. For instance, getting bogged down in trivial actions can slow a game down and make it tedious; if you have a single cutscene to get the PC out of bed, dress him, eat his breakfast and brush his teeth, you've skipped twenty or thirty turns of boring the player.
As a tool to control the emphasis of a game. If most of your gameplay is mainly focused on, say, detailed forensic archaeology, then it significantly alters the tone if (for instance) a fistfight is modelled along a complicated combat system. If you go to a cutscene as soon as the first punch is thrown, it lets you get back to the archaeology quickly. Just make sure that the things the PC is doing outside cutscenes are at least as interesting as the things happening in them.
Avoiding misdirection of players. An author may not want to implement every twist and turn of the corridors from the front of the Secret Service building to their boss' desk; that could suggest to the player that exploring the building is important, whereas in fact all that needs to happen there is a single conversation in a single place. In this kind of situation, it makes more sense to throw in a cutscene as the player enters the front door, and move them immediately to the office. Similarly, if a player can't influence the events of a cutscene, fully implementing it might give him the false impression that he could.

Reasons To Avoid

If overused, cutscenes can cause a player to become disassociated from the game. If all the important action, plot development, NPC interaction and so forth happens in cutscenes, and the actions taken by the player are relatively trivial, there will be little opportunity to engage with the plot. This effect is likely to be even more pronounced if cutscenes routinely hijack the PC, having him carry out actions without player input.
Cutscenes share all the disadvantages of the textdump.
A game overladen with cutscenes can effectively become a hypertext novel with brief, unimportant IF interludes.
If moving from one scene to another, it may not be necessary to use a cutscene at all; a fade-to-black can sometimes work just as well.

See also discussions about cutscenes on the rec.arts.int-fiction newsgroup.