To add to wobble's post:
Captains who are forced to move to the RHS due to a fleet wind down (no command vacancies) and retain their Captains pay are required to bid for every LHR command and also every LGW command (assuming they were previously based there) every year if they want to retain the command pay and can expect to be moved if a command vacancy appears - even if it's not on a fleet of their choice. Fair enough IMHO as it ensures they still want to be Captains and if not, they revert to the appropriate FO pay.
Sure, the money is very good compared to an FO but it doesn't necessarily give a huge amount of stability.