If the audience gives you two different suggestions in response to an ask for, is it possible to combine them? If the first suggestion is dull, maybe wait for the audience to give you more suggestions so you can combine them into something more interesting?
If the audience gives you two suggestions, like "cake" and "auto mechanic", it is usually a bad idea for the emcee to combine them, because it robs the players of potential to have fun and score points with the audience. If the emcee coldly rejects one suggestion and the players throw it into the scene anyway, they get a big cheer. If the emcee combines the suggestions into "And now, let's see a scene about a mechanic who fixes broken cakes," he has deprived the players of the chance to make the most important move in the scene. If the emcee's combination of suggestion]s gets a laugh, this pretty well dooms the players because it simultaneously raises the bar on them and uses up comedic potential.
Also, once the audience has said the suggestion, the players' minds are churning on ways to make a scene out of that. The players might have an idea that works with their own peculiar imaginations. For example, a player who thought of doing a scene where a cake-delivery truck breaks down might have done a lot better with that. When the emcee combines suggestions, it boxes the players in to the emcee's imagination--particularly undercutting if the emcee won't be playing in the scene. Also, a player is less tempted to go for a quick laugh in thinking of how to combine suggestions, which tends to create more comedic potential.