Locos need both, if they don't FILL their aircraft, they move the asset to another base or route. Ryanair and easyJet have a long track record of closing profitable routes because they under-perform. They're laser focussed on high volume, low cost, high ancillary and high load factors. So when people talk about a route working with seats blocked off it's not music to the ears of locos unless they have an amazing airport deal on fees. As soon as that runs out, the dynamics change and the routes get cut, sadly Ryanair do this at a few of their bases.
Look at easyJet at EMA and SEN or Ryanair at BHD vs. BFS and SEN, also Ryanair PIK vs. GLA.