What do relative-to-national trend maps *actually* tell us?

This sub seems to really love the maps that show county or state trends relative to the national trend. Like this one. And particularly of course, the 2020-24 maps where this calculation gives you pockets of red here and there, but mostly swaths of blue.

It's probably too late to ask, but the ostensible purpose of these maps really escapes me. We're taking a summation of very disparate local trends, and then comparing then back to the local trends, which doesn't seem to me to actually say much of anything.

For instance consider the results for the following two counties:

So Trump made significant gains in Los Angeles, and held serve in Leslie KY (he actually improved slightly but I'm rounding the numbers). Of course Los Angeles County, and places like it, have a much more significant effect on the aggregate national trend than Leslie KY, and LA County ends up being pretty solid red while Leslie is pretty solid blue.

But does that actually indicate any kind of meaningful trend whatsoever towards Democrats in Leslie? I don't see how. A reasonable characterization is that Leslie is just about maxed-out in terms of its Republican support. It is a fact that Los Angeles moved more to the right than Leslie, but it is not an interesting fact. And these aren't like cherry picked outliers, I'd say they're relatively emblematic of the red and blue you see on the map.

I'd hesitate to say that these maps are completely void of meaning, but whatever meaning it seems very limited and contextual.