Well considering their natural habitat's humidity ranges from 45-70 year round, your just trying to replicate it. The whole deal about humidity is for overall snake health and good sheds. If it's too dry, you could start to have wheezing from stuck shed in the nostrils, which can lead to other things. When it's too wet, you could have RI's and scale rot.

Just try and get the humidity to around 60% and you will be set, but misting only lasts for so long, that's why most people use tubs.