One of our guidelines at Check Point is to never touch a user's policy structure during upgrades, even if we think it could be optimized. This is because our customers' trust on upgrades and on our management servers is important. So after upgrading to R80.10, all your rules, objects and their enforcement will remain the same, only with nicer colors and better performance.
That being said, things that could change are:
1. Deprecated applications - will remain in the policy but introduce install policy warnings (in R7x these applications were also deprecated)
2. Incorrect database values, such as letters inside a service port number, will fail the pre-upgrade verification process and give you a chance to fix it prior to upgrade.
If you would like to have your policy optimized prior to upgrade, you could use SmartOptimize as described in the video above. Without SmartOptimize your policy will remain exactly the same after the upgrade.