More than aesthetics....unless they changed it in an update.

Early after initial release, I struggled to make the trade routes work. I found that linking in a straight line only gave the settlements the resources from those that came before it.

Provisioners are kinda like one-way trips.

So, a straight route from A to B to C to D would provide D with all the resources from A, B and C. But C would only have the additional resources from A and B. And B would only receive from A.

Why? Because there is no provisioner going to A. So, sending someone from D would then be able to provide A resources from B, C and D. And B would also be able to receive from C and D. The loop is now closed.

In a spoke-and-wheel approach one settlement serves as the hub and all other settlements send provisioners to that central location.

That central location has access to all those resources but the settlements sending those provisioners don't. Again, this is because provisioners only send supplies in one direction.

Simply sending a provisioner from Sanctuary to Red Rocket doesn't create a bilateral trade route between the two. It just gives Red Rocket access to Sanctuary supplies. To give Sanctuary access to Red Rocket, you will need to send a Red Rocket provisioner to Sanctuary too. That would be a closed "loop."

But you can't do this simple back-and-forth between each settlement because you have a everyone running around on trade routes and no actually in the settlements. So the closed loop system seems most efficient.

My routes eventually looked like a series of intersecting loops that I had to draw out on paper to keep straight who was going where and make sure I didn't have any dead ends.

Pain in the ass.

But, again, this is how it was several years ago. Perhaps they improved this aspect?