skyocus, I have to disagree. When you are VFR-on-top on an IFR flight plan, you are no longer afforded IFR separation. If IFR separation had to be applied, there would not be a single operational advantage I could think of for a pilot requesting a VFR climb.
Keep in mind though airport operations and LOAs may prevent these procedures from being applied.
That tracks with what I'd heard about Caldwell. What I truly don't understand, though, is the spirit behind such an LOA.
Case in point, you can be stuck at CDW waiting for 15 mins for an IFR release while they launch jets out of nearby MMU, and props out of N07 (Lincoln Park, non-towered). If it's a nice day, why NOT let the IFR guy launch out of CDW with a VFR climb if he says he can do it.
Instead, the pilot is literally trapped on the ground, not allowed to go. If he does opt to launch VFR, the LOA (apparently) states that the IFR plan should be REMOVED from the system. I just don't get it.
It's actually EASIER to depart from N07 under such circumstances (I do VFR release on IFR flight plan 1/3 times).
My original question, though, is whether ATC was happier to have a specific constraint on the VFR climb (ie. "I can maintain VFR until reaching 4000", or "I can maintain VFR until [first fix on flight plan]") versus a generic "I'll depart VFR"). It seems like it's not anymore helpful, though, as the reason for the denial is not for lack of specifics, but more to do with the presence of an LOA which prevents the action flat out.
Fascinating stuff! I'm always looking to learn more about the most efficient way to get in/out of N90 airports.