It sounds like you got the same invitation promotion that I got. What it means is, until November, you can list as much as you like up to your listing limit and not pay any insertion fees, instead of paying insertion fees once you go over your 40 allocation.
The account I got it on only has a limit of 30, so I'll use my main account as an example. That account has a listing limit of 510 a month. That means I can only have listed and sold 510 items each month. Of course I'm not going to list that many because like you, I refuse to pay insertion fees, so only use my 40 freebies (and other free listing promotions that come up).
If I'd got this promotion on that account, instead of only being able to use 40 free listings before getting charged, I could list 510 things and not pay insertion fees on anything. It just means if you want to go crazy and list a heap more stuff without having to wait until next month you can. It runs until early November.
