My name is Tsahi Etziony, I am the Director of Product Operations at Check Point, and I'd like to explain.
We are aware that for quite some time there is a mixup between major upgrades, minor upgrade and Jumbos. starting R80.40 and the upcoming release of R81, we are trying to make thing clearer with the enforcement of the numbering convention - a major release version number will be an integer (i.e. R81) and a minor release number will be a fraction (i.e. R81.10). So now you'll be able to easily distinguish between major an minor versions.
The most important difference between major and minor versions is the support duration which is based on the major releases and can be viewed here.
As for the content and the upgrade considerations:
Both major versions and minor versions include new features and content - we always strive to introduce new features and capabilities, and every new version contains novelties. Jumbos also may contain new features, but with our careful consideration in order to minimize changes in behavior and any risks to the customer's environment. This is because we see it is as highly important for every customer to always be aligned to the latest GA jumbo, no matter what version is installed, even the most conservative customers.
The upgrade process to major and minor versions is the same - CPUSE creates a new root partition where the new version is installed, and the configuration is copied from the old version to the new one. This ensures that any installation failure or problems with the new versions can be easily reverted by returning to the older root partition which is kept as a snapshot. There is downtime, since a reboot is always needed, but cluster upgrades can keep the system up with no downtime.
Hope this help. I'd be happy to elaborate more if needed.