STABLE marker on functions with single select

hi,

We have some plpgsql functions that return a setof rows from some tables by a single query, they are quite simple. Only
theapplication invokes these functions to query the database, one at a time. e.g. select getFooById(1) 
Do I correctly assume that marking the functions as STABLE will not have any effect on the performance in this case?

Thank you,
Laszlo