It doesn't matter a whole lot, with my laptops I rarely ever turn them off. Always in sleep mode. But since the rMBP has an SSD if you were to shut it down it would only take seconds to boot up. Don't stress this too much, you won't ruin your new Mac.
^^ Yup, aside from maybe saving some battery life and fewer battery cycles, won't make a difference and shouldn't really affect performance in anyway over the life of the computer.
Most people tend to shut it down about once a day (at night), i shut it down when i'm not going to use it for more than an hour. Its up to you, it's designed to fit with most usage types.
It doesn't matter a whole lot, with my laptops I rarely ever turn them off. Always in sleep mode. But since the rMBP has an SSD if you were to shut it down it would only take seconds to boot up. Don't stress this too much, you won't ruin your new Mac.
Personally, I shutdown when i go to sleep, and keep it in sleep-mode during the day.
Then again, because it's a SSD, it only takes 10~20 seconds to boot up. so it doesn't really matter, it's all personal preferences