If opener bids, say 1 NT, his partner becomes the team "captain" on further bidding because the NT opener has strictly limited both his point count and "shape" with such a bid. That is, partner can bid 2 clubs (Stayman) or any number of "transfer" bids, and opener has to rebid the appropriate suit.
But suppose the opponents intervene, and the bidding goes:
South 1NT West 2 spades North pass East 3 Spades.
North has (s) Jxxx (h) xxx (d) xxx (c) xxx. Is it North's prerogative (captaincy) as to whether or not to double, knowing that South has at least 15 hcp and (probably) xx in spades? Put another way, should South refrain from doubling on the off chance that North has both a Yarborough and a void in spades, even if South has good spades?