My twopenneth worth.
It depends (for me), what Is easiest/best finnish. If im fitting a 'square' tray, I'll put the tray down 1st and tile round it, if curved, tile the whole floor (using off cuts under the tray) & fit the tray on top.
Reasoning, when fitting the shower tray, I try to get it as low as possible, most trays I fit are 40mm high, by the time the subfloor & tiles are down, this can reduce the 'step' by about 20mm. This is can be achieved easily when working with a square / rectangular trays.
When fitting a 'curved' tray, I find it much quicker/easier to tile the whole floor (no need to mess about working out and cutting curves, although you don't achieve that 20mm reduction, a 40mm step is more than acceptable.
Footnote:- I'm able to make this choice, only due to me doing the refurb, start to finnish, I get to choose what's best for me over all.
Footnote 2, Silicon seal the tray perimeter irrespective of which option is chosen, movement will still happen in either case over time.