I usually pay for 2 extras, one containing glamour items and rare dyes, while the other stores some housing items and rare mats. I don't constantly change glamours and unless I am in a crafting spree I don't need them monthly, so sometimes I don't renew. I recently got a 3rd one to store Garo gear, but don't plan to renew this one.

That said, I wish I could manually chose which retainer to renew. Because if I want to renew just my 2nd, I am forced to renew the 1st too. Unless I am missing something...