In short, yes it is okay but then again it really depends on how heavy of weights you're using and if you're training for strength or endurance. Is it very effective if you're training to failure for strength with heavy weights? Not really. Training shoulders on one day and chest/triceps on the next is alright for hypertrophy/endurance training, strength not so much. What would be a big mistake in my opinion is training triceps to failure on one day and hitting chest heavy on the next. You will really limit the quality of your chest workout by doing this. Your chest will scream for more but you just won't be able to execute due to weak triceps. I think there are many options of putting together good split routines that don't involve primary/secondary muscle repetition without at least a days rest in between. And always remember, if you're training day to day always hit the bigger muscle group first and do the secondary next. For example, monday-chest / tuesday-triceps, monday back / tuesday-bicep is a much better sequence than monday-tricep / tuesday-chest or monday-bicep / tuesday-back. Big muscles first, smaller muscles second, always.