Professional Skills are skills which cover a complete profession. They represent the high level abilities and experiences that someone who works in that field would have.

For PCs, they are mostly useful for interacting with members of these professions. Though a PC may never actually want to be a Servant, taking the Servant profession skill would allow them to blend in with the household staff without being noticed, which may be useful for infiltration.

Such skills can also be used in place of guile when trying to bluff whilst posing as a member of that profession. Generally, if you look like you belong where you are, doing what you are doing, then bluffing with a profession skill will be easier than bluffing with Guile.