The pros are you can now lift more weight.
The cons are you can now damage the tractor more easily and push it way beyond what it is rated for.
We've had this discussion before. Some folks say, it is your machine, so modify it to suit your needs. Others will say you should have bought a larger machine in the first place.
I say, be careful no matter what you do, but don't be disappointed if you crack the tractor in half, buckle the lift assembly, bend your attachments beyond recognition or get injured when something just plain snaps. /forums/images/graemlins/shocked.gif
If we beef up the machine by adding weights under the guise of making it more stable when lifting the rated 800 pounds, we eventually become use to the new capabilities of the machine and ignore that cut off point. So we try to lift 1000, or 1200. And that worked, so we throw some more weight on the back and go for 1500. Then the thing breaks, the load comes crashing down and property damage(or worse) happens.
I've done plenty to push my tools farther than they were designed to do. Most of the time it works out OK. Sometimes I've paid through the nose to fix the problem that I caused. And sometimes I have been injured(remember my post about dropping the mower deck on my toes?). Just be careful and use common sense.
[Up on my soap box now!]Get the proper tool for the job, rather than pushing it past the design limits or be prepared to be a test pilot.[And down off my soap box!]