What does request and leave mean with respect to Supercell's clash of clans ?
I have seen too many clan description as request and leave!
As far as I can tell, the objective of the members of those clan with 'Req and Leave' (or 'Req and GTFO') is to gain exp/complete the achievement (the one which requires a number of Clan troop donating) for gems.
It's just for the decorations unlocked through leveling/for the achievement since level in COC doesn't affect War/Farming.
Request is to request for troops using the "Request Troops" option which can be selected after tapping on your clan castle.
Some clans impose restrictions and rules on troop requests as there are many people out there who clan hop or repeatedly ask for troops without giving anything in return.
Leave is to pretty much leave a clan, which is the big red button in the clan information screen.
Most clans want active players so that they can win wars. It is frowned upon when leaving a clan half-way through a war as it means two less attacks for your clan.