It is not about speed gain (in case of SQLite) - it is about conversion which takes place implicitly. One must know that passed strings must not be UTF8 strings, so conversion won't hurt them. This is neither
Conversion to UTF8 doesn't hurt anything (except space).
checked nor documented, and even if documented, it forces user to do something to fullfill this requirement.
The user won't have to do anything, since the strings will be decoded on extraction.