It lessens the amount of moisture the plant can exhale.
The crux to cloning is maintaining the moisture content until such time she can bring water up from from the soil, which means roots.
Plants have stomata. These are small openings on the leaf which allow moisture (among other things) to escape.
View attachment 2413308 (There's zillions of stomata, pic is to illustrate my point)
Less leaf=less stomata=less moisture escaping.
Dome+spraying= high humidity= less moisture escaping.