There was a time when I traveled to tournaments. With that level of commitment, it made sense to develop a lot of understandings, many conventional. With a lesser level of commitment, I am less sure.
Yesterday I played at a club with my (more or less) weekly partner, we do not play 2/1. As near as I can recall, the fact that we were not playing 2/1 did not affect the result on any of the 24 boards. He also does not play Drury. I like Drury very much, but not playing Drury paid off here. I opened a fourth hand 1S, he bid a natural 2C and with a fit for his clubs and a strong spade suit I went directly to 4S. They did not find the right lead and with my spades and his clubs I took 13 tricks. Some luck was involved. We usually do well, this time we did badly for a variety of reasons, but none of those reasons would have been fixed by a convention.
Miscommunication is rampant. I always agree to play DONT but if there is not time to discuss it I simply hope that (1NT)-2C-(X) doesn't arise. It did arise with this f2f partner, we do play DONT, and we have discussed this. After the X the way to get partner to run is to XX, a call of 2D is natural. Larry Cohen agrees. If two DONT players have not discussed this, I would say there is a fine chance that the 2D bid over the X will be misunderstood, either intended by one as asking for a run and taken by the other as natural, or the other way around. As it happened on this one, I had clubs so no run was needed but if my stiff spade and my four clubs were, instead, a stiff club and four spades I would XX. partner would bid spades. With long diamonds I bid 2D over the X and partner will pass.
So my objection to conventions is really an objection to agreeing to a convention without adequate discussion.
Added: I just looked up how that 4S making 7 scored. Not well. I have Kx of hearts and the A is on my left .We can make 6NT as long as the spades come in. I have AKTxxx and partner has the stiff Q. They come in. Nobody is in six ov anything, but 3NT makes 7 unless the heart ace is led at trick 1. Oh well.