The traditional Bodybuilding Workout Split has, unfortunately, become the default routine in most gyms. While a 3 or 4-day split is great for building mass, it is an inferior way to look slim and defined.
This site is dedicated to the lean and slim Hollywood look, so of course I am going to recommend an alternative to the typical routine. An athlete in peak condition can teach you much more than a sluggish bodybuilder.
Bodybuilding = Break Down the Muscle + Rest and Nutrition
If you think about bodybuilding in simple terms, the goal is to lift with enough volume and intensity to break down the muscle fiber in a muscle group.
Following the workout, the muscle then needs to rest to repair itself.
Adequate protein and nutrients need to be present to ensure a full repair of these fibers. Done properly the muscle fibers grow in size.
Over time this leads to visible muscle growth.
Training the Entire Body Each Workout?
This would be bad for bodybuilding.
The problem would be that the workout would have to be extremely long to ensure enough volume of lifts to break down the muscle properly.
Another problem would be that the muscles worked last in the routine would get neglected due to fatigue.