Smith is a quality reliever. His injury last spring was an underrated part of the Giants forgettable season. Without Smith, the Giants did not have the type of reliever who can be consistently effective against left-handed hitters.
Bruce Bochy likes to play match-ups late in the game, and he needs relievers who can be effective against either handed batters.
However, Smith is not a LOOGY-type reliever. Similar to Jeremy Affeldt, he can pitch a full inning, and is not vulnerable to platoon splits. Unlike Affeldt, he is not prone to sustaining injuries in hilarious and inexplicable ways.