Don't use much, and most uses are for things like tuna or salmon salad, or as a coating before crumbing for oven-frying. Why use anything but Hellman's for that?
However: when I want something special, such as a rouille, I definitely make my own. It's the only way to get the specific flavorings I want. At work I used to have to make tons at a time, so I did it with a stand mixer fitted with the balloon whisk. But I don't have to make more than a cup at a time, so I've taken to the blender method for ease: drop egg yolk, acid, mustard, etc. into blender cup. Blitz. With motor running, slowly pour in oil until desired consistency is reached. Stop motor. Taste and correct seasoning. Blitz a tiny bit more to mix. Pour/scrape out into storage container. Bingo!
(Sorry, I rarely measure when I do this -- "to taste" and "to the desired consistency" are the only rules.)