Originally Posted by
Vessbot
Careful with the specifics. While still on vectors and not yet intercepted a leg of the approach, you're not on anything "published" and cannot descend.
Correct, better paint the full picture.
During vectors ATC becomes responsible for the terrain clearance (which does not remove the pilot's one for the very same). Implied in the question is the fact there already was an altitude clearance.
In that full scenario the altitude from the last clearance is kept until over the IAF and then descent as needed (CDO) is approved, not below the procedural altitudes.
In my experience any radar vectors /direct to is usually accomplished with an altitude clearance same as the ensuing procedural altitude after the intercept location.
I. e. the case for the OP's question would be "Direct IAFFO, descend 4500 ft, cleared for the approach." Where after IAFFO 4500 would had been charted until the next step.
Or a different one specifically reiterated such as
descend and maintain 6000, direct INFIX. After INFIX, cleared for the approach, descend as published.
While not formally required, it shows a good understanding of the cockpit HF from the ATCOs.