Ignore "plays that don't matter". That's a very hard statement to define, and could massively affect your answer.
The other answers are talking about "same contract leading to same result". Which is one answer and a very useful one. But it hides the hands where, for instance:
- one declarer got a friendly lead and took the obvious tricks, but the other declarer got a bad lead and hand to execute the pentagonal squeeze to achieve the same result;
- the defenders, on the run of the diamonds, pitched the relevant card to allow pickup of the rest of the tricks, where at the other table the defenders played perfectly but declarer guessed the end position right anyway; or even where
- declarer played it like a fish, but the opponent's revoke, and subsequent one-trick penalty, brought them back to average.
But not only that. As I have made clear in other answers, in my most common partnership, I play an anti-field system (K/S, with 12-14 NT). That means that whether or not we end up in the same contract (from the same side, even), the auctions on all hands where we open with 12-17 HCP and balanced distribution will almost certainly be different than at the other table(s). And that means that the information available to the opening leader will be different. And that means, often, that the play of the hand will be different. Even if it results in the same score, does that mean that "the play didn't matter"?
And the pair that plays Precision. Or opens weak 2s on J-sixth. Or plays Suction over NT vs DONT vs Meckwell vs Landy vs Natural. Even the pair that plays coded 10s and 9s, or odd-even discards, vs the "standard" players.
Yes, there are hands where "all roads lead to 4♠ and there are three unavoidable losers". From my experience, they come up maybe 4-5 hands in a 27-board set. And even then, only 1-2 actually are flat-across-the-room, 0-1 if there are more than say 6 tables in play.
One of the things that make expert players expert is that they can win a match 25 IMPs-3 with the same hands that I play to a 5-3 "winning tie" (and one of those swings was "1♣-1♥; 2♥ vs 1NT-p" and the other was "1♣-1♥; 1NT-2♥ vs 1NT-2♦; 2♥").
Another thing (very obscure) to think about is the difference between matchpoints (frequency of wins) and IMP (size of wins) play. There are "boring" hands at both styles, but in a 60-board IMP match, they might not think quite as hard about the overtrick in 3♥ (where it might cost 1 IMP. A "well-played" scoreline in world-class competition is "2 IMPs a board", so say 75-55. Fatigue over that 1 IMP might cost 10 down the line) as they would in a 101-table matchpoint game (where the difference could be between 65% and 35%, and that's the same as the next hand's difference between -100 and +420). Or they may not compete as hard, knowing that it's wrong 15% of the time, but when it's wrong, it's -1100 and 14 IMPs (versus "a bottom, but the 50% of the time it's right, we gain half-a-board).
So the number of boards where "the play doesn't matter" could be very different on Saturday (the two session Open Pairs) and Sunday (in the Swiss), even if they were the exact same boards (played by two different sets of people, of course).