As others have said, your minimum speed to maintain control and steering may be different than someone else's minimum speed to accomplish the same thing.
Many times I have gone through a channel and all it takes is one extremely slow boat to make it very difficult for those behind them to maintain control. Most people go through the Weirs Channel maintaining the same throttle position for the entire channel. They should be adjusting for the different water speeds such as when they go under the bridge and it narrows or even when they get out by the beach on a windy day and more speed is necessary to maintain control.
Again, different boats react differently and some are more affected by wind and current than others. If you are in a Channel and there is no one in front of you for 200 yards but there are 20 boats in line behind you there may be a message there!
Too many people operate both boats and cars as if they are the only one out there and all they need to do is look ahead of them.