I absolutely agree with Sandy and gdjoslin... if no one shows up at a chair or group of chairs for 30-40 minutes, I remove the stuff and take the chairs.
It drives me insane sometimes to see how people "reserve" deck chairs... I've been on deck taking sunrise photos, and people will come up with their book, towel and a bag, drop them on the chair and walk off for hours. I've even observed a person "reserving" chairs on BOTH SIDES of the pool - so that they can shift back and forth as the sun shifts. How ridiculous can you get?? That's just not fair.
There's plenty of chairs on board, and you may have to "tolerate" a short walk to the pool, but so be it!!