In the context of what you are explaining, yes you do ++get every 10th value++ but in actual fact, when running low-write emoncms ie feedwriter, you would in fact get the first value in any 10s window.
Feedwriter will only update the feed once and then not update further, ie not over write existing values. Whilst standard emoncms would in fact write the given feed value window 10x, once each time the 1s input is updated so it is only then that you end up with the last value jn eazh 10s window.
But yes overall that sounds pretty much it for fixed timeseries feed data.