A little bit of occasional playfulness adds to ease of working in tense environment.
Tension does not in anyways bring additional seriousness. If anything, it only adds to the environment becoming further unbearable and non-conducive to performance. Nothing grows in gloom. A good leader knows when to ease the environment and make the air around lighter to breathe. Infact, that bonds people together and makes the preassure easy to bear. Wit and easy humour are great tools that an effective leader needs to cultivate. But a safeguard for the wise...do not end up making that into rowdy & boisterous moments. A leader does not have to be a stand-up comic. But light humour and clean playfulness (not pranks) adds to his effectiveness. I always believe...no fun, no learn. This is similar.