[awm]

The advantage comes in when opener has ten cards in two suits. If the third suit is a fragment, then when opener holds 6-4-x-x or 5-5-x-x his next bid just shows the tenth major suit card. This is problematic because finding the shortage is often important to slam bidding (and just became a lot harder) and because opener is making pretty frequent use of a higher bid (i.e. 1♠-2♣-2♥-2♠-3♠) instead of the cheaper minor suit bid. In general the location of the singleton/void is probably more important than the tenth card in the two suits where opener has shown nine cards already.

[DCal]

I am going to bid stayman. Assuming opener bids two diamonds, I am going to jump to 6 hearts. It's probably wrong, and more than likely too aggressive for IMPS, but I don't see any other way to get to a probable slam. I would assume that partner, sitting on three spades and two hearts, might guess to "correct" to 6 spades, but what the heck. I like my chances in the slam.
Obviously, if partner responds with a major, I'll be a little more circumspect.