Just to add a little more... the IAF marks the point at which the Pans Ops (or any lower) speed limits come into force. The IF will also tell the pilot that the next fix will be the FAF, where an even lower speed limit will apply, therefore the pilot might need to start slowing down from the maximum speed that is permitted in the Initial Approach segment.
Additionally, the IAF marks the point at which the width of the protection area reduces from the width associated with the enroute phase of flight. Depending on whether or not a STAR is used to join the enroute and approach segments, there may be other changes as well (ie secondary area).
The IF then marks the point at which the width of the lateral protection area progressively reduces even further. And, of course, the FAF marks the start of a further, progressive width reduction occurs. Thus, the pilot MIGHT see obstacles at a rather closer range, without getting toooooo nervous about them!