Android Log.v(), Log.d(), Log.i(), Log.w(), Log.e() - When to use each one?
The Android Studio website has recently (I think) provided some advice what kind of messages to expect from different log levels that may be useful along with Kurtis' answer:
Verbose - Show all log messages (the default).
Debug - Show debug log messages that are useful during development only, as well as the message levels lower in this list.
Info - Show expected log messages for regular usage, as well as the message levels lower in this list.
Warn - Show possible issues that are not yet errors, as well as the message levels lower in this list.
Error - Show issues that have caused errors, as well as the message level lower in this list.
Assert - Show issues that the developer expects should never happen.