I think the 'expansion gap' is to allow for, erm, expansion, so 5-10mm is usually recommended. I'd say, that in a house with heating, the extremes of temperature probably won't cause expansion of more than a few mm at most, so 5mm should be ok. The gap will hopefully be concealed by beading.
Moisture can create problems here though, and if a room is damp, then things can get a bit tricky. Hence, most types of laminate flooring aren't recommended or bathrooms. Not ideal anyway, as it's too slippery when wet. Better off with floor tiles or textured vinyl.
I have seen examples of when no gap has been left. Interior landscaping, anyone? 😀