I look at friendlies as practice. If it's too laid back, I don't get into the complicated situations and nuances I normally would so I don't learn anything. This is why I also hope my opponents in the friendlies see it this way - you will both get more out of it if you're both applying yourselves. Luckily, you can usually snap people into it by beating them badly over and over lol (which will happen if you are playing more seriously which is required to practice properly).
Of course, it is fun to sometimes just have a laugh and do whatever. I don't think it's bad to do that, and I definitely do it myself sometimes, but I think it would be silly to say I am not having fun when playing serious, too. That's the whole reason I play the game in the first place.