It does have a number of uses, yes. For trainees, knowing the DMI can help determine the projected salary for next season. That is, if a trainee has proficient game shape, the DMI allows you to calculate his projected salary.
On the other hand, for players that are not trained any more, you can calculate the exact game shape (e.g. for a player with strong GS, whether it's 8.1 or 8.9) from the DMI and the salary.