Usage increase is equal to the computation time of marker updates. Every time you update map markers, some computation is required to calculate the optimal position of the markers. The compute is provided by an API endpoint which is used by the library internally.
Example: Updating the map with 100 markers takes 10ms of compute time. Your usage will increase by 10.
Usage is billed at the base price times million milliseconds per month.
Example: You are subscribed to the Pro tier, and your usage is 25,000,000ms for a given month. Your bill will be the $5 * 25,000,000 / 1,000,000 = $75
If you use the same markers on your map multiple times, subsequent compute requests will hit the cache and the usage will be greatly reduced. The cache is invalidated after a certain time depending on the subscription tier.