Insulation - partial/full fill

[Mojooo]

Can someone clear up some points for me i nrelation to insulation that goes into the cavity of (newly) built walls for houses.

I understand that the insulation boards that you can buy are partial fill - so you need to leave an airgap - does anyone know what happens if you don't leave a space? Damp? What if the wall is sheltered - i.e there is no chance of it getting wet from rain.

I understand the mineral roll type stuff is full fill. A buidler I was talking to says you need to leave SOME gaps because the way he does it is build a few course of block/brick and then put the insulation in - and you need soem leeway to actually squeeze it in. So my query is ocne it is in, if it is not crammed in touching block and brick on either side does it matter too much?

I woudl have thought a smarter way to have done it owuld be to build the block, then put the insulation in and then build the brick - that remvoes the issue of trying to put something between the gap and the ties being in the way.

I have been gettign conflciting advice from builders hence my queries.