Marcin, As I remember, there was not always need to assign new tags immediately to keep them alive.
Even now I can create emty tag this way:
- new tag created (without assigning to any photo)
- immediately use it as gallery filter (empty result)
- tag persists!
For me, it makes a sense to create system of tag(s) in one session and use them later.
I think this rule "use new tag immediately" is pure technical limit (or bug). Common programmers practice is: "Documented bug becomes a feature".
I am not sure, if your tip is: "allways clean unused tags".
But my tip is: "make creation of new tag less tricky".
edit
...and wait... I made a test, and now I created new persistent tag even the easiest way. Simply created new one. Perhaps the bug is removed.