Good question. Basically the higher the hub score the more exposure HubPages gives your hub.
There is more information in this guide:
The majority of my hubs are somewhere between 70-90. I've never had a perfect 100.
If you are looking at which Hubs make the most money the HubScore is not always the biggest factor. In fact, only one of 2 of my top 10 high scoring hubs actually make a significant amount of money.
My highest paying Hubs are scored between 79-86.
That being said however none of my lowest ranking Hubs make me any sort of substantial money.
I write Hubs for two reasons first because I enjoy it and second because it makes me some extra money.
I use the HubScore to help guide me in writing a better Hub. If for some reason the Hub doesn't rank that high I try to figure out what I am missing or did wrong to try to get it to rank a little higher.
My goal is 80 or above for each Hub but I don't always get there. Any Hubs that rank lower than 80 get a little extra work once and a while until the HubScore improves.