We are looking to replace our microwave. We have a set place it can go which is inside a set sized cabinet with an opening out the back for ventilation. 

Every Microwave we have had, says it requires SO much space on all sides, even if there are no vents at the top or sides, and because we have no choice we have picked the best one that requires the least space and put it in the gaps. 

This time around the microwave we want is 42l but only marginally larger than our existing 32L model. Right now we have about 4cm on each side for clearance, next to nothing on the top but oodles of space behind. This new model will give me about 5cm of clearance total but there is a vent only on 1 side so we were thinking we would slide the microwave off center to give it 5cm on the side with the vent. 

The question is, how big a deal is a recommendation to have big spaces all around the microwave? This particular microwave wants 10cm both sides and 10 at the top. There is simply no way we could accomodate any sized microwave under these conditions. 

What are the downsides of ignoring this? I mean we have had to on the MW's we have had previously, but they were a little smaller than this one.