Almost never.
With that group we mostly played 2e, so I don't think we ever threatened to reach the level limits. If you happened to roll well enough to play a ranger or druid, you played a half-elf to multiclass it. Everyone wanted to play the elusive half-elf druid/ranger.
Somebody in the group did the math showing that you were never that far behind a single class character, so it was our conventional wisdom. Nobody liked triple class though, for some reason.
Only if you wanted to play a paladin did you go human or single class, and most of the time that only happened if the DM spotted the player a 17 for Cha.