Question
Our gardener wants to plug our marathon grass at least once a year and I always thought marathon wasn't a grass that spread out and didn't need aerification.  Do we need to do it, is it a good thing?

Answer
Plugging a lawn is a fairly simple and effective method of filling in bare areas or even replanting the whole lawn. Here is a copy of what I have previously recommended.
 "If you decide to plug the lawn, mow and then spray the weeds with glyphosate ("Roundup"), or any non selective, non residual weed killer. Allow three days at least (a week is better) for the product to work its way to the roots. Use a plugger that matches the size of plugs and make a row of holes, add a teaspoon of "Milorganite" and press a plug into each hole. Repeat the routine until the whole area is plugged. Walk the whole area afterward, stepping on each plug to ensure it is tightly in place. Water the area well and keep at it until the plugs are firmly rooted in. Plugging is best done and most fun as a team effort, family or friends.
Just in case I did not stress it enough let me emphasize that you must have a way of providing water for germination and establishment if you use seeds or rooting in if you choose plugging or sodding. If not, you are setting yourself up for failure."
I have no experience with 'Marathon' grass but it appears to be a variety of Fescue.