Making how much batter will result in over-mixing? This page, tip #9 &quot;Don’t Double the Recipe&quot;  suggests that making too much batter results in over-mixing, and, consequently, in a dense (as opposed to fluffy) cake.
Is it correct? Could you give some guidelines on how much batter is too much? E.g. for crepes mixture? Or for flour:sugar:sunflower oil:milk 1:1:1:1 batter, 1 egg per 50g of flour, batter?
The amount is only restricted by the capacity of the tools you have at hand.  The point is, don't mix too much.  If you have a bowl, filled to the brim, you will have to mix a lot more to get all of the ingredients incorporated.  If that same bowl is half full, a few quick strokes is all it takes to mix. Over-mixing risks building the gluten structure too much, which results in a &quot;tougher&quot;, less light, final product. Bakeries, restaurants, and catering services probably do more at once than most people do at home...it is just that they have larger capacity tools.