What a fascinating question; I have to admit, I had not thought about it that way.
Well, while I believe there can be some caps from taxes or other specific benefits from a few other plots - the overall "benefit" of the mod - is to enjoy it.
The new features, new ways to build settlements - new buildings and plots to explore.
For me, I love seeing the things I have set up (i.e. I said "put a plot of this type here") take root and grow - seeing the variety of building types upgrade over time, seeing the settlements (and new NPCs they attract) turn into thriving (or struggling...as the case may be) communities.
To me, that growing town is a lot cooler than a bunch of shacks with bunk beds thrown into them and turrets, generators and water pumps everywhere....
(not that I might not still do that ...once in a while).
Now, also, as I enjoy a bit more of challenging survival experience, I also like the more realistic ideas of settlements needing supplies and help, as I find the base game a bit too easy in terms of scrap and caps ... so for me, if you configure (up to each player on their own of course) them to do so, the settlements can actually be a resource and cap drain .... which I enjoy. But hey, I am a bit of a glutton for punishment in that regard (kind of like volunteering to clean the kitchen for the weekend....oh boy).
There is also a sense of discovery in unlocking the advanced plots and capabilities (see the tech tree in the wiki...), and of course, in SS2, the new story unfold.
So, the benefit - I guess it depends on what you want out of it, it can be a different experience for everyone.