Is there anything worth doing in those forrests that show up after you get out of the Underdark ? Does it mater whe you explore the areas in relation to the Critical path of the story line ie. Bohdi ?

ther is a mini quest in one of them but othre than that they
are pretty useless. There is nothing relating to the major quest

One of them, I forget it's name but it's the one on the right, has a little sub quest with Coran and Safana from BG1. You'll meet Coran in the top right corner of the map outside a cabin and he'll ask you to help him rescue Safana from a pack of wolfwere's.