It's not just for text based stuff, although that is a good reason. Ideally, it should be used for all websites if at all possible, for reasons such as:

Websites going down (which is what happened with this Stone Toss comic), stuff being stealth edited (or in the case of a certain One Angry Gamer list, taken down altogether with no warning), and for another object of personal contention relating to posts here, twitter posts and/or accounts just going <poof> and being left wondering what was said because they posted a raw link and not an archive.

Finally, as an honorable mention, archives can, if timed correctly, not only be used to preserve history, but also act as evidence of what we used to have prior to clown world.