Any job requires attention and concentration. Even in this case, there will be mistakes.
I'll be honest, I spend 4 hours a day testing the game for all the functions in the game! Even in this case, I find mistakes in the game. Therefore, performing such tedious actions every time you can avoid mistakes.
The written code is also strongly affected, if it is a complete mess, it will be a pain for the developer. Even the last generation of my code, which has a perfect polish, even in it I make mistakes due to lack of attention to work.