I'm not sure to what degree it matters. Getting room requests granted depends largely upon what is available when rooms are assigned, IMO. Disney CM's try to accommodate requests but it isn't always possible. We try to book something where, even if we get the worst possible room (which has happened to us) in that category, we would still be happy enough to stay there.
That said:
Early check in is a room request, I believe. If you have other requests that are important to you and an early check in is not important to you, then I wouldn't request an early check in. (JMHO, of course and may not matter at all)
We usually have some requests (like room location or balcony type) that we care more about about than when the room is ready. So we almost never ask for early check in. WE prefer to go to the parks or the pool and just wait for a suitable room to be available. We do like to arrive at the resort as early as possible in order to have the best chance of changing the room assigned to another one that might come available later that day, if necessary.