Character Sheet Privacy
For my part, in twenty years of gaming I've never experienced any of the downsides of sheet sharing the others here have seen. I've also never found a situation where it was better to hide character sheets from other players than to show them. Here are the "why would you do that" thoughts in my own head.
If any players are learning the game. There's no better way to learn than to play, and you learn faster if you can see how things work any time anyone does things, rather than just waiting to be helped along only when you're doing things yourself. You might not even need any handholding if you can see someone else do stuff, or you'll at least know what questions to ask to smooth your understanding. Also having players assist each other with learning is much faster in PbP than always having to wait for the GM to be available.
If the players ever need to plan something. It's incredibly helpful to know what skills and abilities the other PCs have, and waiting for them to volunteer that kind of information can take a lot of time in PbP.
If anyone's playing a new character type before and might make mistakes along the way. Kinda like with learning the game, learning new things about a game you already know is much easier when you have help from people who've done that before and know the pitfalls.
If the players are human and might make mistakes. Forgot you have seven spell slots since leveling up instead of six? Accidentally rolled the skill level of a character from your other game because you were thinking about something else when punching in the numbers? People make mistakes all the time, and they're easiest to fix when anyone can point it out and keep things moving smoothly, rather than relying on the GM to have to be constantly vigilant for every type of problem that might come up because character sheets are private, in addition to all the other GM duties.
Are there really so many problematic players ruining RP by seeing each other's sheets that the issue is rampant enough to warrant people wondering why anyone would ever share a sheet? That's a lot of missing trust that should be there in a group.