counterpoint (don't take this to seriously):
there are to many types of bricks to sort by form. unless you have an inventory the size of a brick factory you can only sort by category or by size.
otherwise, sorting by color makes your collection aesthetically pleasing, and when you build, you usually want to use specific colors only to make your model look good.
That's why you have to group similar forms. - Bricks - Plates - Narrow Plates - Wheels - Windows/Doors - Smooth pieces - People bin
And then if you like to sort further you sort out the smallest of each bin because those always fall to the bottom when mixed together
sorting by size needs to come first. from my own experience, you can't find any small pieces if they are mixed/covered by larger ones.
There are less different forms than any normal brick enjoyer has bricks of a specific color. Therefore the lookup is faster ;)