Singers have a limit to the amount of singing practice they can do each day ranging from 10 to 20 mins for beginners to 60mins (and sometimes 2hours depending on the singer) for professionals. More singing than that in a day is really not recommended for anyone. There’s only so much you can do during that time and if you have a lot of music to work through, or you aren’t feeling well, this means progress will be very limited.
Luckily mentally practicing is a great way of getting around this. Even though Adam Neely talks about playing the song on your forearm, us singers don’t even need that. When thinking about the song, our muscles in our throat will automatically do very tiny versions of the movements that they will have to make when actually singing, which means that you’re practicing. It’s very important for a singer’s intonation to mentally ‘hear’ the notes before singing them and this practices that skill as well. Adam will later go on about practicing by humming. Please be aware that, even though it might not feel like it, it’s still singing and will tire your voice. Mental practice for singers is really about hearing the notes inside your head without singing them.
Why practice loudly at all, I hear you say? Stamina is something that needs to be built. It’s very useful to imagine your route before going for a big run. Knowing where you’re going is going to make the run much easier, but it doesn’t mean you’ll be fit enough to actually do the run. It’s the same for singing. Knowing the notes is only part of the physical activity that is singing. The movements need to be practices and ‘worked into the voice’ as well.