Lockpicks are an excellent tool for gaining access to the contents of locked rooms or chests when one does not have the correct key. These tools are useful to "jimmy" such impedances. However, if the lock is too complex or the door magically sealed, then either a spell or a rare skull key must be employed.
One deficiency these picks have is in their durability; If the user is either too clumsy or attempting to pick an un-pickable lock, the lockpick will break.
In the earliest Ultima games, only guards had lockpicks, then known as keys, meaning the player had to kill them to get access to certain areas. By Ultima III, lockpicks became available from any guild shop, and this would continue until Ultima V; although in that game, lockpicks could be obtained from treasure chests.
From Ultima VI to Ultima VII Part Two, they were know known under the name lockpicks, and worked the same as previous iterations. They were also readily available since many tool shops sold them.
NPCs never seem to object to you jimmying their locks, with the exception being Ultima Underworld II.
In Ultima VII Part Two, Shamino tells the Avatar that the lockpicks should only be used for virtuous reasons, because the Avatar is no common thief... yet he and the other companions still don't complain about their leader stealing.