If they're no longer required (despite what the tournament info says), fine, and I don't normally care if playing sayc opponents who don't have a card open. But in that case, the requirement to have a convention card should no longer be listed as a requirement.
I was particularly annoyed in one recent ACBL tournament, and asked for an explanation of every bid, because opponents ("experts" of course...
Now, you might think, who cares about convention cards if you can just ask what any bid means? Two reasons, first it slows down the game to ask each time, especially since some opponents tend to be slow and/or incomplete in explaining (and with private chat, other opponent may draw inference from delay, while p is ethically obligated NOT to draw any inference...which can lead to p being overconscientious and not making the bid that he/she would have made had their been no delay...).
More importantly, asking may give your opponent the information that you care what the bid means (which may lead to an inference that you have length in the suit bid, or a greater share of the outstanding points than your partner, or whatever). Similarly, having to ask what defensive leads/signals mean is also a significant delay, and again lets opponents know that distribution and/or location of particular cards may be significant, which may encourage deceptive signals to prevent you from reading the hand...
Oh, and of course, a surprisingly large number (still a minority, in my experience) of those who explain a bid, "accidentally" tell the table (and thus their partner) what the bid means, instead of only the opponents. But that's another topic, bad alerting/explaining...

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