Yeah, very few hard rules, but some rules of thumb...
There are some workshops that can get "cluttered" - butcher shops are a classic. Mason shops rarely (w/ newer clutter math), but still not impossible, depending how (in)efficient your Haling is. Nice to be able to keep working while you designate a spare workshop for deconstruction, then simply rebuild it and have the items moved aside and be back in business.
Some shops are used for multiple diff tasks, as mentioned above - Farmers and Craftsdwarfs being primary, but the occasional Mason etc as well.
Also, quite often I'll have "training" shops for no-/low-skill Masons or etc. Keep makin' dem blocks, boyz! (These will often be dropped in the middle of a mined-out area, just for convenience.) Also useful when mass-production is needed, such as for blocks, mechanisms, cages, trash trade goods (for example, stone mugs), etc.
For Glass and Pottery, you need maybe ~3 extra shops to have "Gather sand/clay" orders for every 1 active workshop producing products, to keep that in constant supply. (Note that these do NOT have to be "powered", so can be non-magma, np.)
For key workshops, I also like to have multiples in case of Strange Moods, so a dwarf claiming a shop will not bottleneck that production chain (and so I can lock the ones up front and force them to claim the one in the far back corner!).
And, depending on how much I'm micro-managing things like Levers for color and/or Beds by preferred wood, I'll drop a workshop immediately adjacent to that part of a stockpile while going for that goal just to shorten the hauling process for the craftsdwarf.