I hate working Saturdays for residential as the kids are off and so they get under your feet. Also my wife is off if I have to spend the day with her, my mates are off if I want to spend the day with them, sport happens on a Saturday if i want to take part or watch it. Also I find as you get busier you will take a Monday off if your working the Saturday but will usually get a emergency call which goes into the Monday slot.
I do charge extra purely because i dont want to work it (although I dont tell them I charge extra I just give a price).
I never work Sundays.
Mark