I'm a kit guy, so that's where my experience lies. My understanding is that the must in the primary should be stirred well to ensure that everything is mixed and that oxygen is mixed in. Then the yeast is pitched, and then it is not necessary to stir, unless there is something floating like fruit or cheesecloth bags. And then I just stir whats on the surface under.
Not really needed. What is needed when fermenting in a plastic bucket LAY the lid on top w/o airlock. If doing fruit wines then you need to "punch" down the pulp 2X a day.
Some kits do say to stir thou
Any wine with fruit in it needs to be punched down to prevent the fruit from rotting and to let the enzymes get at the fruit and extract the flavor and colors. Stirring it until it gets down to about 1.025 will help get 02 to the yeast which is detrimental to a healthy fermentation. I use an lid and airlock on my fermenters but do stir at least once every day and punch down also if I have fruit in there. Once it gest down below 1.020 or there abouts you should cover the fermenter or rack it to carboy with airlock to stop the yeast from multiplying causing them to concentrate on eatingup the sugar and turning it into alc.