EasyJet aren’t like Ryanair.... crew apply for their chosen base. They don’t get told where they are going by easyJet.
But if you mean operationally, if they are required elsewhere they can be sent wherever. So if you are LGW based, you could be sent to work out of BCN for several days but as they are LGW based, it is a ‘trip’ and is treated like any other layover.