I say use placeholders and prepare once whether or not your statements get executed once or a hundred times, not necessarily for performance reasons, but just because its 'the right thing to do(tm)'. You don't have to worry about quoting your values correctly, the database itself might be able to cache the statement, thereby saving some database load if anyone else runs the same statement and/or the same script, and I know of one database that used to have a bug where if the same statement was prepared over and over too many times, it just didn't get prepared successfully anymore (now that was a hard bug to find).

Ok, if the database is MySQL, then there's no real performance gain, but at least the code is more ready for another database that does benefit from such things. At least use prepare_cached w/placeholders if you can, which is the 'easy way' to prepare once.

And what PsychoSpunk says above about RaiseError.