Castle early, castle often!

"Vote early, vote often" is a piece of advice that often pops up around election time. And with the (Australian) Federal Election on tomorrow, it may be the only thing that will save the Liberal Party from defeat. (Attempts at "False Flag" operations having blown up in their faces).
Years ago I appropriated the saying and turned it into a piece of advice for junior players. "Castle early, castle often" I'd say, to the confusion of those in front of me. "You can only castle once" would come the challenge from the more learned children. "Not necessarily" I would reply. And as evidence I present the following semi-famous game.

Heidenfeld - Kerins, Dublin 1973

1.e4 e6 2.d4 d5 3.Be3 Nf6 4.e5 Nfd7 5.f4 c5 6.c3 Nc6 7.Nf3 Qb6 8.Qd2 c4 9.Be2 Na5 10.O-O f5 11.Ng5 Be7 12.g4 Bxg5 13.fxg5 Nf8 14.gxf5 exf5 15.Bf3 Be6 16.Qg2 O-O-O 17.Na3 Ng6 18.Qd2 f4 19.Bf2 Bh3 20.Rfb1 Bf5 21.Nc2 h6 22.gxh6 Rxh6 23.Nb4 Qe6 24.Qe2 Ne7 25.b3 Qg6+ 26.Kf1 Bxb1 27.bxc4 dxc4 28.Qb2 Bd3+ 29.Ke1 Be4 30.Qe2 Bxf3 31.Qxf3 Rxh2 32.d5 Qf5 (D)
At this point Heidenfeld forgot that he had already moved his King (by castling!) and castled again, on the opposite side of the board. Sadly such imaginative play did him no good.
33.O-O-O Rh3 34.Qe2 Rxc3+ 35.Kb2 Rh3 36.d6 Nec6 37.Nxc6 Nxc6 38.e6 Qe5+ 39.Qxe5 Nxe5 40.d7+ Nxd7 0-1

(This game was sourced from Tim Krabbe's Records Page, including the helpful colour tags showing the 3 castling moves)