There isn't a single document that has the information you're requesting, but hopefully you find this response useful.
Major releases (8, 9, 10, etc.) are typically when there are significant feature additions and updates to the software suite.
Point releases (9.2, 10.1, 10.2, etc.) may include some feature additions and updates, but on a smaller scale compared to the major releases. These releases would also include bug fixes for issues found in the previous release. Note that these are full installation packages similar to major releases.
Updates (10.1 Update 2, etc.) contain bug fixes for issues found in the previous release and are cumulative so only the most recent update needs to be applied to its appropriate release, unless otherwise stated. Note that these are NOT full installation packages and do require the appropriate point version to already be installed.
Whenever a new update is released for the core Laserfiche suite, the Rio and Avante download packages on the Support Site will be replaced with a newer package that contains the latest updates. We are working to standardize this across the other products as well so that when you download the latest version of the software, you won't also have to manually apply any updates.
Here is a general white paper regarding upgrading to Laserfiche 10. It covers major release upgrades.
KB 1012113 contains a list of the current release versions and updates.
Point release upgrades are done in a similar fashion to major release upgrades. For example, you can just install the version 10.1 software on top of the existing version 10.0 or even 9.0 software.
Updates must be applied to the appropriate software version. For example, you cannot apply Laserfiche 10.1 Update 2 if you are only on Laserfiche 10.0.
On occasion, an official hotfix may be released through a KB article. These are for critical out-of-band issues that have high impact. The application of the hotfix may require manually replacing files. These are rare though as the software update release cycle is usually sufficient.
In terms of pitfalls to watch out for, there really aren't any since these upgrades are meant to be able to just be applied on top of already installed software. It's recommended to backup the databases used by the software (repository, Forms, Workflow) as there might be schema changes and so if for whatever reason you need to revert to a previous release, the database backup can be restored and used.
Also, if upgrading to Laserfiche 10 from a previous major release, please make sure that Windows Updates are fully applied first. This should be done in general, but is especially important for Laserfiche 10.