DPI does not affect jpeg file size. Number of pixels does, as does content (more detail bigger files), noise, iso (because of the noise), quality setting etc.Makes sense, I have no excuse for my senility
But I can understand the notion because pixel processing software like LR seems to make makes a large fuss about dpi settings, but it only matters for import into desktop publishing and is irrelevant for other print/screen purposes.
I don't think LR makes a large fuss over dpi, it is just a tag. But it is what gives you your print size unless you deliberately specify something different, and if you still have a version of PS that has the "Print View" option in the zoom settings and you have set your monitor up correctly then it gives you a pretty accurate WYSIWYG idea of your print. I use Print View all the time and that 100% is driven by dpi.