Well, it was the last minute touch and go that we had expected from Wenger but Diarra's transfer continues to be a bit of a headscratcher. Wenger calls him a multifunctional midfielder. Diarra has so far been utilized as a right back for Chelsea.
I don't know what role Wenger sees him playing exactly at this point because he already has Bakari Sagna on the right who is coming along faster than expected. Wenger probably wants to employ him as a holding midfielder who will eventually replace an aging Gilberto, but this adds onto a crowd of players operating in the middle of the field.
Some like 21 year old Abou Diaby who is enormously gifted has seen limited action and I thought Wenger would concentrate on developing him, if he is not really interested in getting any more wingers, rather than add on another central midfielder.