Although all activeCollab releases are important, some are just more important than the other ones. They can be divided into two groups:
Another thing makes branches important: it's the access to the files as part of your Upgrade and Support plan which is tied to them. What this means is that you get access to all releases in all branches while you are in Upgrade and Support plan. Once you get access to a branch, you can download all smaller releases within it. This lets you have access to the most stable release within a branch even when your Upgrade and Support plan expires.
Let me explain with an example: *
You decide that today, October 6th 2008. is a fine day to purchase activeCollab. Now that you have a license purchased, you get access to activeCollab 1.1 branch and its latest release, plus one year of upgrade (expires on October 6th 2009).
Spring 2009 comes and we release activeCollab 1.2. It's all great because you are within Upgrade and Support plan and you get instant access to this branch.
In September 2009. we release activeCollab 2.0 and you get access to that branch also. Because of that, you still get the access to all 2.0.x releases even when your plan expires. If we release activeCollab 2.0.2 in November 2009. you’ll be able to download it even through your Upgrade and Support plan expired a month ago and you didn’t renew.
Couple of months later we release activeCollab 2.1, but this time you don’t get access to that branch because your Upgrade and Support plan is expired - the latest release available to you is the one which belongs to 2.0 branch (precisely, to the branch that was actual at the moment when your Upgrades and Support plan expired). To get access to this new branch you’ll need to renew your subscription for another year.

Additional information about Upgrade and Support services and branches can be found in this knowledge base article. If you have any additional questions, don’t hesitate to ask.
* Dates in this example are not real. This is not activeCollab roadmap!
If you have something important to say about the issues discussed in this post please write at hi@a51dev.com.