>if you start calculating in occasional and intermittent loads for fuse ratings the fuse is going to end up vastly over-rated for the protection required.
If you read the whole thread, you'll see that a common fuse used is 15A. After about 1967 or 1968, all new British bikes were fitted with a 17.5A 'continuous' fuse. The next-lower values are either 10A or 12.5A respectively; from first-hand experience they are either completely unsuitable (10A) or "nuisance rupture" (12.5A). Otoh, in the event of an actual short-circuit, either 15A or 17.5A will blow.