In my own experiences I think I never had such bets offline but online I am not sure or maybe the opposite. I don't really had time to memorize all my bets but it could be that I am just betting one sports at a time mostly in combat sports but only offline. I think the risk of losing is high on this strategy but may also have the higher chances of winning due to the numbers of category.
I am the same, as far as I can remember, I have never done betting on different types of sports, and the most I do is bet on football. Maybe the most frequent is multi-betting on different leagues. (same). Lol
It requires good focus in my opinion, because we must have good knowledge of the sport we are going to bet on, besides that we also have to analyze the strengths of those who will compete, it will require long consideration.