What are the disadvantages of Monovision?

In monovision we create a distant eye and a reading eye. As a result, the depth vision may decrease or the distance vision may be less good than usual (especially in twilight/dark). For example, some people still use glasses when driving in the dark.

Also, the reading eye is not good enough to go your whole life without reading glasses. You will always benefit from the reading eye. Your reading glasses will be less strong.