I think the use of some industry tags can be useful to complement the occupation tag which I find to be too broad.
When I find a record of an ancestor's occupation I am always delighted because it often gives me leads into new record sets to seek. Knowing the ancestor had an occupation is not nearly as useful to me as knowing the industry that occupation was in.
At times I think it might be useful to use tags for the actual occupation, like miner, mining agent, toller, etc but as you can see from this first example such tags quickly get very granular and less useful.
On the other hand an industry tag of mining would help group them together for any mining historian who was browsing our site and has their interest piqued by the first mining question they see.
The use of an industry tag such as mining is not intended as a method for replacing a search using the term "mining" but instead the use of industry tags is put forward for discussion as being a way to achieve more granularity about specific occupations than the occupation tag allows without going to overly granular occupation tags for every occupation. However, searching for questions using an industry "term" is one way of trying to assess whether a new industry (or any other type of) tag might be before coining it.
Some other industry tags that I could envisage using are:
I would not try to be too prescriptive about how "big" an industry has to be before it warrants a tag. Like all tags their existence should be organic, if they are useful they get used and stick (and warrant tag wikis), if not, they fall into disuse and tend to be removed.