Client Settings
Common Settings
Vault Locking
There are two common settings - when to timeout, and what to do when it gets timed out. The above should be self-explanatory. The settings are different for the Browser Add-On which allows for the timeout to be the screenlock and/or a computer restart. The mobile app allows for an App Restart timeout.
Change Master Password
There are options on the other clients to do this, but they redirect to the web vault.
Web App
Display layout
This allows the web vault to display using the whole width of your screen. Just a nice QOL improvement.
Browser Add-On & Mobile Client
Server URL
Your URL should include the `/bitwarden` path at the end of the domain.
Unlock with Biometrics/PIN Code
This allows you to log in using a PIN or biometrics (fingerprint reader on mobile, etc.). This is much more convenient after setting up a device than having to re-type your master password over and over again.
Dark Theme
The only sane choice.
Auto-Fill
The explanations are above, but I would suggest setting these the way that seems best to you.
Note that if you don't have the URI saved for a site, but are using Bitwarden anyways, it will prompt you to add it to a new entry instead of the existing one.
Sync
This is to manually sync the clients. However, the clients sync any time there is a change as described in https://bitwarden.com/blog/post/live-sync/