The key phases of the room selection process are as follows (each described in its respective article):
Group Suite Selection vs. General Selection
The iron rule by which selection runs is very simple - square pegs must fit in square holes, no exceptions. In order to run an efficient, clean, and unmessy selection process, selection occurs in two passes. In the first pass, Group Selection, students who have registered as groups pick their housing options. This is where the Indiana Jones and the Last Crusade-esque decision comes into play. When your turn comes and no suite of corresponding size is available, your group is essentially 'dropped' into the second pass of selection (though keeping the same seniority value and assigned lottery number when generating the General Selection order) and must pick into singles and doubles that were leftover when groups of 2 ran out (the only size of which there are more rooms than groups) on your own in General Selection.
Because lottery numbers have been assigned to everyone in advance, is possible for groups to 'count' and deliberately drop into General Selection. This happens in two cases typically - senior groups with incredible lottery numbers dropping into general so that all the group members pick a Watt studio single for themselves, and Sophomores who want singles but hedging their bets. A sophomore group of 2 can count ahead before their turn comes in Group Selection to see if there would be any singles left by the time everyone ahead of them in General Selection finished picking. If yes, they can drop. If not, they can select a double together, a room that will almost undoubtedly be better than the double they would have picked into blindly during General Selection, because it would have been a leftover.