Limited major openings allow responder to raise to game on a wide range of hands, forcing the opponents to guess whether to get involved. In Precision, responder can raise a major to game with three trumps and a balanced 14-count, or shapely 5-card support and a weak hand.
With Scamp, you miss out on that quick 5-3 game raise but more than make up for it with the quick 4-4, 4-5 & 4-6 raises, which are much more common.
Should South have either doubled or bid 4S? Probably but that could catch East with a 4-4-3-2 14-count.
At other tables, the auction often went
1D – (no) – 1H – (1S)
2H – (4S) – 5H – end
