Seeking a long term relationship with a special person is a serious matter, but life is no fun if people are not able to laugh with each other. Getting thrown curve balls on a fairly regular basis is a normal part of life, and getting through the tough times often calls for a sense of humour. Sharing it is one way to cement the relationship, so the need for laughter is a reality. Being able to chuckle or even guffaw over the silly things that can happen in life is what makes it fun to have a partner.
Little things often occur when a group of people get together, and meeting a person's family for the first time is fully of them. The roast might be done to perfection, but the potatoes could be a bit soggy. Apologizing for them could be embarrassing, but a funny story about another cooking event that went wrong can make life easier for all concerned. A serious relationship needs at least one person able to salvage a situation like this.
Going out with a person leading into a serious relationship can involve meeting their circle of friends, and gaffes can often occur because people are anxious to make a good impression. Someone might mispronounce the person's name, but taking it in stride can make everyone relax. It can turn a slip of the tongue into a lifelong laugh for everyone, and that alone could help the relationship prosper.
Laughter throughout life is an important component to keep away depression, and it helps people see that not everything is a serious occurrence. Being able to laugh as a couple shows two people have found their way to communication that matters, and they should be able to solve almost any issue that crops up in their future together.