My wife and I have one set of shared bank accounts (checking, bills, savings), and that's it. Ever since we got married. She had her own account for like a year or so after we got married, but she didn't use it, we were just too lazy to close it for a while. We swapped over her paycheque early on.
I dunno, man, we seem to be an outlier, cause the idea of maintaining separate finances as a married couple just seems so... alien, to me. It quite literally never occurred to either of us, as an option.
Downsides include that you can't really keep secrets. For example, I know how much she spent on me for Christmas, and where from, she's just not gonna give me the receipt until next year.
And yeah, if we ever divorced, that'd probably be a problem. 12 years in, I don't think that's happening.
Anyway, if keeping separate finances doesn't seem weird to you, I don't see much downside. As long as you CAN agree on who should be responsible for what, seems entirely manageable to me. Biggest upside for joining up, I would think, is less legal work for you each to get access the other's assets, in the event of a death or similar event.