What is function of stacking gel?

Answer 1

From what I have been reading, It helps concentrate or stack the loaded samples in a tight band before it's resolve in the resolving gel. Notice how when samples are loaded into wells, it sort of spans the wells, so by concentrating it before separating gives the sample a fair start. And you can have a result that shows uniformity not one that's comparing bands which started at different points. Hope this helps!