Is it better to workout one part of your body or more of it?

by this question I mean that when you workout, is it better to do,for example:legs only for the day and do chest or shoulders another or is it better to do for example:chest and cardio and arms all in one day? I always do cardio because I need to get rid of my belly fat and grow some abs (: but I usually do shoulders,bisects, and triceps afterwards, is that bad?