A loss of inhibitions is more likely. It's easier to pick out good ideas from a large list than a small list. Idea evaluation is often easier than idea generation, so give yourself lots of ideas to analyze later. It's easier to create a good idea from combining lots of little ideas. A fast output of ideas reduces the likelihood of evaluation and so helps a loss of inhibitions.
People get more absorbed by the process and think more freely.
Quantity, in this case, brings quality. The focus on each idea is minimal at this stage and so participants feel less pressure on each idea. Wild ideas can be turned into valid solutions. You encourage others to put forward stimulating ideas by using those ideas. You build freedom for yourself when you put forward stimulating ideas.