File>Export>Export As: Quality vs. Scale

I am trying to arrive at a rational strategy for outputting my images to jpg's which can then be batch processed to yield files of more or less uniform size.  I understand that different client or other sharing needs will necessitate the custom sizing of files on a case by case basis, but it still seems like I need to have a unified strategy for the initial output of my images.

Therefore, I arrived at the following solution:  Output the files to large jpgs which can then be batch processed to smaller ones depending on the needs of a particular project.  For example, if a photo contest wants all my files at 1860 pixels on the long side, and files under 1 mb, I can create a Batch process that will give me more or less uniform sized files for that project.

To that end, my question is, does this seem reasonable?  What are others' practices?  And specifically, so the title of my post is not completely irrelevant, what does "Quality" refer to precisely in the Export>Export As feature?  I know that Scale refers to the size of the Image in pixels (making the image bigger or smaller in terms of pixel size) but what is affected by Quality?  I see that the file size changes when I change Quality but not the image size.  What exactly is being changed in the image to  make it smaller or bigger?

Thanks,

Barton