FOR leaner TAGS only
1) Rename Alternate Spellings to a single. eg. SiFi, SciFi,SyFy,SF
2)Remove redundant stuff that is unneeded in Calibre. Author names, series names that some indies load thier Tag with .
2b)Remove redundant tagging left over from paper catalog days. Romance-Historical, Historical-Romance.
If you see a dash, 90% of the time, you might use tip 4 instead
the computer can find ANY use of a tag (fragment) so there is no need to put 2+ tag versions when the one contains the term
3) (always struck me as absurd) Fiction-Science Fiction. IMHO If it is not non-fiction, assume it is fiction. (or the flip if your library is mostly non-fiction)
4) Hierarchical Tags (and series). Science Fiction.Military/
The primary tag is the general genre , the later is a refinement. If you standardize (clean) your tag before adding to the Main Library (use an Intake Library to massage the data first).
My 2cents
'Assumed' Tagging might trim them even more.
Historical.Agriculture.South US <non-fiction
Vs
Romance.Historical.South US <<Fiction because of the Primary