Extrinsic proteins in plasma membranes are like a flotilla of boats because they can move relative to one another but usually only in one plane, some may have masts / flags for signalling like glycoproteins / receptors, the proteins are held in relation to phospholipids like boats in the water.
Salt in the water has a role in stability /density of the sea as does cholesterol and the interactions between phospholipid tails in the membrane.