Fish come from a vast number of different habitats and adapt to those local situations in ways related to many different considerations, such as safety, potential food, comfort and social relationships (in the literature, within-species social and sexual reasons play a much bigger role than one might initially think.)
So it's very hard to generalize from the point of view of the fish. Backgrounds are mostly all about humans often trying to create a beautiful image in their homes. It is true however that many fish will indeed feel a greater security and less stress if they have both background and plants available as options for protective cover. It has been observed that a greater density of plants actually encourages shy fish to display in the open more often.
~~waterdrop~~