Drylined a few bedrooms and always left a small gap before plastering to allow for expansion and skirting covers gap.

About to start on a bathroom which will be tiled onto directly, (floor and wall), possible some tanking in places. (but only around the bath).

Whatever i decide to use on the walls, whether it be aquapanel, waterproof plasterboard etc, would i take it right down tight on the floor or still leave a gap?

It would do no harm to leave a small gap, imo 2mm or 3mm. Not in a wet room situation though, most tanking tape will only cover 1.5mm gaps

Just reread my post and worded it wrong, nearly all tiled but only around the bath.

But was thinking of tanking some places.

But if tape is only 1.5mm, wont i need to take it right down to the floor???

Only for a wetroom /shower room, some tanking kits only allow 1.5mm gaps for tape to cover. If it's not in a shower enclosure you could leave a bigger gap and use silicone. Not with the Impey tile safe though it reacts with silicone

if using plasterboard mercedism, leave a gap between floorboards and plasterboard ( I usually pack up with a plasterboard off cut) this stops any damp off the floor seeping into the wall pasterboard

Same as Doug for the same reason