The vast majority of easyJet aircraft W patterns are driven for utilisation. So you have the likes of FAO-SEN-AMS-SEN-FAO where the Faro based aircraft doesn’t have time for two full round trips from base but does have time to fit in a quick Amsterdam and back. They used to do something very similar on TLS-BRS with an EJU aircraft and more. It looks to be about balancing short and long sectors in the aircraft working day.
There is very little of this at the UK bases as those already have a mix of short and long rotations at the bases, without needing to export aircraft elsewhere to get it.