Pgbench with -f and -S

Pgbench allows -f and -S combinations together where the doc says that -S effectively uses the internal select-only script. 

Is it okay to assume that -f is disregarded here? Or are they run in round-robin fashion (although then, how does it know which read-only part of my script to run?) or something else like that?

Effectively, I think it should raise NOTICE that -f is useless here.

robins