Stove maintenance will varying due to the nature of stove types, pellets used, and settings. The manufacturer's recommendation is to be followed, but a stove that is running inefficiently will need to be maintained more often with at the very least a good cleaning. This is in order keep the efficiency of the stove from dropping further. Yearly checks in spring and before fall are recommended to ensure a happy heating season. You absolutely don't want any part of the nightmare that is to be trying to schedule an HVAC specialist when the weather turns.
Anecdotally, with a high quality softwood pellet and their stove tuned in, we've had customers who have gone an entire season without emptying their ash pans. I don't necessarily recommend deviating from cleaning at least once a month, but a quality pellet and a complete burn do wonders for your stove. You can check out the pellet they used here.