PG Phriday: EXCEPTIONal Performance

Like any programming language, the PL/pgSQL Postgres procedural language has plenty of handy control structures. Among those thankfully modern accoutrements is the humble EXCEPTION block. While not the more prevalent try/catch methodology, we can use BEGIN anywhere to start an embedded section for the same effect. Knowing this is the case, what are the costs of actually using them? Postgres is fairly streamlined, and as such, can take several shortcuts when there are no exception blocks within a chunk of PL/pgSQL.