hi Nicolas
this is now documented in the latest 8.5 (and i think 8.4) CLI guide, it says:
This parameter helps increase the one-time pass ratio for client association especially in a noisy environment
which is a bit vague.... I have asked techpubs and engineering to try and come up with some better wording for the CLI guide, but untl then, see below.
This knob was added to provide relief for an issue seen with handheld devices, AP-3xx access points and a busy/noisy RF environment. The command has no effect on any other models. When it is enabled it increases various timings/retries etc. used during assocation so if the client is a bit slow/hesitant or the environment is noisy (thus causing retries, contention delays etc) then there is more grace given during association and it is not deauthed for taking too long.
hth
-jeff