It matters most for cancellation purposes as well as for coordinating add-on contracts in the future. For ease, it’s best to have the same use year. Then again, for folks who are traveling multiple times a year it may not matter too much. But it’s more to keep on top of with different deadlines.
As far as cancelling, you want to have a use year that is as close to your usual travel time as possible. So that the points are available juuuuuust before you go, and so that you then have most of the rest of the year to cancel your trip and use the points so they aren’t lost.
For us, we travel mostly in April. Ideally we would get a Feb use year. We can book the points for April, and they will be available in time to travel. But if we need to cancel - what is it, under 30 days? - and the points go into holding, we have allllllllll the way until the following Feb to use, increasing the likelihood that we would get the chance to do so and not lose the points altogether.