Most races encourage drafting and some don't, although there are non-spoken rules, even when it is allowed -- such as share your time at the front and never, ever, bump the kayak or the paddle of the kayaker ahead of you. Breaking either "rule" more than once will have you quickly "excommunicated" from the group, or having cold water dumped in your lap.
That said, I was talking more about sea kayakers in a group who want to travel fast. For some inexplicable reason, even sea kayakers who are trying to set speed records as a team, rarely draft each other, which is a huge tactical mistake, IMO. Assuming that a group has the same level of fitness and capability, if the conditions allow, you can move faster as a group, drafting on the stern and side wakes, than you can travel alone.