A pro to only owning one large contract is that you only have one contract to manage and keep up with. You would also have the 11-month advantage at that resort with all of those points.
The big con to owning one large contract is that you can't split up the contract if you ever needed to sell. Also, if you like staying at different resorts, you would be limited to only booking at the 7-month window if you wanted to stay there. Now if normally always stay at your home resort, that isn't a big deal. But if you like BCV for F&W and VWL at Christmas, then you would probably want to have 2 contracts at each of those locations so that you'd have the 11 month booking window.
Some reasons that people like to get multiple contracts:
1. If they ever need to sell, smaller contracts go quick.
2. If you have 3 kids and want to split up the contracts easily.... have 3 contracts (or enough smaller contracts so each child gets the same number of points)
3. To get the 11-month booking advantage at different home resorts
Can you "pool" your points? Well... yes, sortof... maybe...
IF you have all of your points in the same use year, and under the same primary contract, then those points are all considered part of the same pool at 7 months. However, you can not 'pool' them all together at the 11 month window to book a stay. For instance, if you had a 150 pt contract at OKW and SSR, you couldn't book at 11 months and use 300 pts at SSR. You could only book up to 150 of those points for SSR and then at the 7 month window you could use the other 150 pts to book ressies at SSR.
Ok, now if you have multiple contracts with different Use Years (or under completely different contracts), then it isn't as simple to "pool" the points. You actually have to call MS and have them transfer the points from one contract to the other. Now, this isn't that huge of a deal, and can be done, but there are restrictions and limitations. You can't transfer points back and forth between the accounts. You can only transfer one-way in a given year.
Ya know, now that I've typed so much I can't even remember the question... I hope I might have answered some of what you were asking. I think it's past my bedtime and my brain is starting to shut down.
Regardless, I HTH....