I think it depends on your routine. When doing two consecutive workouts more recovery is allowed if you avoid working the same body part two days in a row. Triceps tend to get worked when you do chest exercises. Biceps when you work you back. So it is generally a good idea to working chest and triceps one day and back and biceps on another day. If you have at least 48 hours between workouts and you are not lifting really heavy, then it may not matter much if you work chest and biceps on one day and back and triceps on the other.
Another theory is that if you just worked your chest, then your triceps won't be 100% when you work them--same with back and bicep. So if you work your biceps when you work your chest you'll be able to curl more weight than if you do your biceps after your back.
I've done a workout split that worked chest, shoulders, and arms one day; legs and back the next day. Even though my biceps and back were worked on consecutive days I still made gains in back and bicep strength. So who knows? As long as you're not overtraining a muscle group you should be fine.
You just need to find what works for you. And when it stops working do something else.
ETA: I just read Kathryn's post.