In bridge, how do you tell when to use holdup versus blocking plays?
To prevent the lead form RHO through your tenace, you want to win the ace when RHO plays his last card in the suit. If it looks like LHO has 5 cards, with three in dummy and your hand, win the second round with the ace. If you have only two in had with three in dummy, win the third round with the ace.

In regards your Club Kibitzer - yes, the proffered advice is in general sound - however, the cardinal rule is always Count the hand. If you have counted the hand, the answer is often obvious and possibly counter-intuitive from the general rule suggested by heuristic analysis.