If i ever do them together, I do them at seperate times of the day. Chest in the morning legs at night. But this is rare and only done is I have to for some reason. Legs are a big muscle and I usually do the by themselves.
I got a question pertaining to legs though.
Do many people split legs into two days, quad day and hamstring day? After squats plus other quad workouts, I usually need to either throw up, or I am so shakey I can barely do SLD's, and other ham workouts very well.