As someone who lives in one state but plays in two others, I see nothing wrong with this. There are reasons to do this having nothing to do with hedging your bets.
I play Virginia day league because it is a rare opportunity to play outdoors in the springtime, which is lovely after months of being indoors. I also like that the level of competition is high and I know none of my opponents so there is no history.
I play DC because the culture there is different. I get to meet different people. I like that the ladies senior matches were at a convenient time and location for me. DC leagues advance to sectionals without the need to go to Districts.
Also keep in mind that different jurisdictions play different formats at different times. The seniors league is in January in MD, but in the summer in DC. There is no singles league in MD, but VA has one for those interested in singles. VA had tri-level years before MD did. On the other hand, I don't like to do VA night leagues because of the traffic and the time limit of 90 minutes.
If I had to pick just one league (MD), it would reduce my tennis opportunities considerably. How is that good for anyone?
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-- Master Moonballer