At one time , the last thing a spark would do, when adding a circuit say, is make the decision that the board needs upgrading. Maybe because they were less affluent times , customer wouldn't go with that ... or the spark didn't want to know , just add yet another sw/fuse , take the money & run .
Another point with domestic work , back in the day it would be rare to find a spare way in a board . I've seen many houses with just a 3 way Wylex ...Lts / Plugs / Imm. Htr .
Spare ways cost money back then , much like installing single sockets , your local contractor would charge double to install a twin SSO .
I've worked for a couple of contractors years ago , who when doing new build or rewire , if theres 4 circuits ...fit a Wylex 4 way board .
Same on industrial , fit a 4 way TPN board so you'd have say , 2 TPN machines ... 1 x roller door..... 2 light circuits ... 1 small power circuit . No expansion catered for .
Thinking back ...that same firm always under estimated trunking sizes ...if it needed ,say , 4x4 they'd send out 3x3 . You would assume , until you learned, that they know what they were doing but it soon became apparent that you were expected to ram a million cables into the 3x3 then get the lid on without crushing half of them .
They had a storeman back at the office , there were certain rules like , you couldn't get a 1/4" drill bit to fit the stupid Enox tank cutters .
They'd give you a 5/32" ...because " Its a 1/4" clearance "
12" x 32 Eclipse hacksaw blade ...no chance ..10" flexible ( bendy) Ding-Dong utter lettuced. ( Remember , all the work then was steel conduit & trunking & SWA ) You could have a 12" only if you were cutting 6x6 trunking . Dear oh dear .
They would actually say ..." You had a hacksaw blade 4 weeks ago , whats happened to that ?" ( Never say it broke ...it always wore out)
Once , when sitting in a traffic jam I was interviewed by the AA for their magazine . I'd got out & replaced a windscreen wiper while waiting .
They put in their magazine , Mr Evans , an electrician returning to North Birmingham , replaced the wiper etc .
Weeks later I was in the office when it was mentioned , they'd read it , "You must have been on the so & so job that day ....we checked the time with the AA as 5.30 so you didn't leave early then !!" Tossers.