For example, when someone asks a question and he is saying
I am using Ubuntu 11.04. Should the question also be tagged
11.04 or not ?
If I see any mention of version (either software version which I lookup on http://packages.ubuntu.com/ or Ubuntu version) I tag it accordingly.
It could be used for determining the age and relevancy of the question. Tags can be used for searching: https://askubuntu.com/questions/tagged/11.04+upgrade
I find the version tag more useful to questions related to upgrades, bugs, drivers and the use of new software like Unity. Software recommendations and shell-scripting questions are examples of questions where the Ubuntu version does not matter.
In addition to what Lekensteyn I use the following ideas myself:
- If something changed a ton, like say unity, I tag those with the versions so that it's obvious which major release people are using, but I don't tag general stuff like apt, dpkg, or something like that.
- Kernel/Hardware/Video stuff for sure since hardware detection is version specific there.
I would definitely avoid adding a version tag just for the sake of having it.
Version tags can be dangerous if the community starts to believe that every question, no matter what, has to have a version tag.
Only version tag posts that provide at least some evidence they are in fact tied to a specific version of Ubuntu.