They're there to prevent racking, so bottom edge of one face of one
joist connected to the top the next face of the next joist - and vice
versa - giving a diagonal/herringbone pattern.

No point in connecting tops to tops or bottoms to bottoms as the
floorboards and plasterboards do that already

I'm less clear on which is superior, herringbone struts or noggins, and
why - in these days of mitre saws, cutting solid noggins to an exact
fit is no hassle.

I thought they'd be fitted by nailing the flat ends to the tops of adjacent
joists so that the strap is 90 degrees to the direction of the joist, i.e.
to replace a noggin... in which case why the circular/hand saw?

Have I totally missed how these are fitted?

Cheers,
Chris