Needle maintainers are those which are necessary to keep the machinery well oiled to run at its full steam; essentially activities which makes sure that there is nothing adverse affecting the product, there is no bad debt (technical or otherwise), the key metrics are not showing anything that is unusually alarming. Essentially ensuring that the product does what it promised to the customers and the cross-functional stake holders such as sales and engineering are enthused about it as well.
Needle movers are those activities which result in creating long-term compelling competitive advantage for the product or creating differentiators that gives the product immense position of strength in the market or targeting a new market segment. Not always (rather rarely) does the activities under this section result in creating something that is of strategic importance to the product; but it is essential to always work towards the needle movers lest the product stagnates.
It is easy for Product Manager to get into the nitty-gritty of things and get sucked into “needle maintainers” and ignore to work on “needle movers” as sometimes it is so difficult to see small success in the activities under “needle movers”. At the same time, it is also possible for a Product Manager to totally concentrate on getting the needle move, but in reality killing the goose that (already) lays golden egg, by not concentrating on aspects that require the product to be well oiled to serve the customers at the best levels possible.
This is not just another case of time-management, but something a lot more than that. It is necessary for one to be a great Product Manager to balance the needle movers and needle maintainers. No suggestions here; it is left to the style of working of each Product Manager.