Hitting a muscle once a week vs. Twice a week

We should also keep in mind that there is a lot more to it than just doing full body, splits or how many times a week you work a muscle group. People are biased against full body regimes, once their progress slows down, they go for splits. However, there are a hundred things you can do in a full body workout. Changing sets/reps, using techniques such as rest & pause, priming CNS, ramping the weight up, changing the volume pairing different exercises, etc. Anything you can think of in a split. It's all about what you need. In fact if you have a weak point, you can train there on a day as if you're doing a split, and do this more than once a week if your recovering abilities are good, while you keep doing full body workouts 3 times a week (excluding exercises which work that specific bodypart). So that would be a combination of splits & full body workouts.

i.m.o , its better to decide on your own...it takes a while for anyone to get to a level where u can really exhaust a muscle group and bring it to a level where the recuperation time goes to five to 7 days... on the other hand once u r already training for more than a year, u r supposed to be able to hit your muscles to a real hight intensity and/or volume at one training session.. the problem is more of psychological.. after 2-3 days of such training u notice a swelling and feel kind of tight inside your skin... and then u don't want to let it go..u feel like hitting them again...
the fact is whatever works..the important thing is to be coherent.. as someone claimed here..he has noticed considerable gains in training twice a week..after more than 2 years..the factor is actually doing it continuously for 2 years... moreover its not a crime to have a fav muscle group and concentrate on it more..its very normal ... i have a similar problem with my arms ..kind of bigorexic about them... but thats my motivation of training as well.. its not a good idea prevent people by telling its wrong...its more important to listen to  your body..and note your progress..
if u see in the next lifting session you r feeling stronger .then why not. But i.m.o, its better to try different types of exercises if u r training twice a week... for me if one day a direct isolation, the other day is compound ones..