Q:

General rules for multi tags and concatenated tags

While reading the topic about cleaning up the android tag there was also a comment from Jeff Atwood to the usage of concatenated tags like android-layout. Jeff said that android and layout should be used as multiple tags are possible.
I asked why the reality goes in the other direction referring to android-intent synonyms but I didn't get any answer so that is why I ask here.
I think Jeff is right and we should use the multiple tagging instead the combined tags but before I start to edit the tags, I was wondering if there is already a rule and if not, if we could formulate one. Also there is help needed from moderators as some automatic tagging needed to be turned off/on depending on the final decision.
PS: I don't want to start a war about tagging :)
PPS: seeing the tag tag-synonyms as a perfect example on how hard it will be to draw a line when a tag is useful and should be concatenated and when not...

A:

Part of the reasoning behind the  android-activity and android-layout tags is that the Android community was co-opting the activity and layout tags to mean something very specific to Android, even though these tags were being used on other questions having nothing to do with Android. The Tag Wikis for these tags even contained language that said they were specific to Android.
To solve the problem, the different meanings for activity and layout were separated into their own tags, such as android-activity and workflow-activity.  To make the whole thing consistent, android-layout, android-intent, and a few others, were added to the mix.  

One reason you might want to make make specific tags is so that you can follow them (you can't follow pairs of tags).  Also, you can't make a Tag Wiki for tag pairs.  
That said, it's still possible to search on tag pairs, and this process is very effective for finding subsets of questions that are specific to a particular concept like Android Layouts. 

