concept of white / negative space, as i said.
a tattoo can have more impact if it's not surrounded by a lot of other 'rivaling' tattoos, so to say.
i mean take that girl as an excample, that palm tattoo pretty much 'stands out',
imagine her having the whole arm covered as well, would be a totally different thing.
not saying 'better', but different.
in the end it's down to personal opinion what appeals more to you i guess.