The problem comes in when you specify some values but leave others at default, as in this scenario, or when you haven't used a feature for a while, and think a default is A when it's actually B.
If you explicitly define each value, you not only can't easily make that kind of mistake, but you've also documented the structure completely in one place rather than relying on documentation elsewhere. This reduces the chance that someone else (a coworker or even a replacement) could misunderstand what the sequence is doing.
Or they can open up SSMS right cilck on the sequence and go to properties and see more information than you'll get anywhere.
Edit: I should qualify that... you could run a series of queries to get the info that right clicking and selecting properties does. Near as I can tell it takes 3 separate queries. It would be nice if sp_help would give all the information. Kind of sad that it doesn't.