There are a number of things that make life easier to handle on this planet, and being able to laugh is one of them. This ability serves a similar purpose to oil; it allows life to flow that little bit easier.
Without oil, a machine would soon end up seizing up, but while the world probably wouldn't come to a standstill without laughter, it certainly wouldn't be the same. Instead, it would be like living a life that is in black and white.
A Gloss
Being able to laugh, then, will be what gives life that bit of extra sparkle. So, let's say that someone is experiencing a fair amount of stress; they will be able to watch something that will help them to relax.