Yes one layer. think of it like this,
you can't erase anything and try not to use CTRL Z, and you will get also learn
how to not only blend faster and blend accurately,
this technique is good as it teaches you to take or make big decisions, and if something goes wrong you learn to work around it.
SO in future projects if you face a problem you know ways to get out, place it teaches you to back yourself and your judgement.