Is it really obligatory to prime a wall when you are going from a overcast color paint to a lighter color paint? ...
Answers: Its extra important to prime a wall if you are going from a see color to a light one. The dimness color will show or bleed through your light color except then you will cessation up unhappy nearly how the paint job turned out. A nice gallon primer is nearly the same as a gallon of fitting paint. If you use primer you can usually get away next to 1 or 2 coats of paint, if not after you will need to do 3-4 coats to return with good coverage over the dull paint.
yes, priming will cut down on the number of coats of the paint you will need, and also a primer will hold on to the dark color from showing through the lighter paint.