I'm not trying to be too much of a pantsweasel here, but the assumption in this question (and all but one of the answers) mostly applies to Centralized VCS, such as TFS, SVN, Perforce, etc.
Fair enough, it's what the OP is using.

On the other hand, however, when using DVCS (such as Mercurial and Git), you usually shouldn't wait to checkin, and most of the things mentioned in answers - such as diffs, get latest, merge, etc - are not necessary. Even things like code reviews and tests are better to do after the checkin (though perhaps before pushing, depending...)
The one exception I saw here (so far) is associating with a work item. Of course, commenting on the checkin is also good...