I tried searching for this answer in the manual but came up empty. I’m confused as to the difference between using VST quick controls and simply midi learning a vst parameter. Do VST quick controls simply exist for the rare (I’ve never come across one) VSTI that does not have midi learn capability? Or is there some workflow I’m missing?
The biggest benefit is that it doesn’t matter what CC the controller is transmitting on. Most controllers are able to be edited to send on particular CCs but it is often difficult. With Quick Controls, Cubase “converts” the Cc # to a QC #. If you change controllers, to one transmitting on different CCs, you don’t need to reassign for each VST instruments parameters. You just assign each knob to a QC number in Cubase and the “conversion/connection” is more transparent.
Hi, it’s me again (not stalking you, I promise! 
)
It is certainly a solution for VST Instruments without their own MIDI Learn (there are certainly more of those than you might have encountered 
).
Direct MIDI Learn does have the possible advantage that the automation is just “regular” MIDI data, and is recorded as part of the targeted MIDI Track/Part, whereas with VST Track Controls, you have to Write-enable the VSTi itself, and is recorded as “Host Automation”, which you’ll then find in the Automation lanes of the VST Instrument (and not as regular MIDI)
EDIT: I see that jaslan has posted in the meantime (with another observation)
Great points again! Thank you jaslan and Vic! Really appreciate you sharing your thoughts!! I think it will take more practice to sink in and figure out my work flow (if I prefer midi automation vs host automation).
Helpful info. Thx.
Here’s an example for the benefit of quick controls:
Let’s say you have a VST and only use the filter cutoff. Then you have an insert fx with a tremolo and a reverb…
And now, let’s say, you have a midi control device with a few rotary knobs… You assing the knobs to the few vst and channel / fx controls you really need - through the quick controls.
Now you have all necessary controls at hand without changing any setups or whatever… Superfast 
Just to add to this discussion for the benefit of inquiring minds…
I recently figured out the difference between Track and VST Quick Controls. I’m alway late to the party. Most times, I’m not even invited. 
My controller consists of two banks of 8 rotary knobs.
Bank one is set up for Track QC beginning with the Cubase default of CC#16.
Bank two is set up for VST QC beginning with CC#70.
Confusion sets in: both banks control QC on HALion Sonic 
At this point, it’s easy to be oblivious to the possibility of user error and point the finger elsewhere…
An EQ and compressor were placed in the Track Inserts. Functions were assigned in the Tracks QC panel.
Now the Track QC knobs on my controller control the assigned plug-in parameters while the VST QC knobs control QC on HS. 
Brilliant Steinberg functionality 
The complete quick control concept is a mess- since they are not native per host midi port available.
Otherwise we could automate them in a midi clip without 3rd-party plugs, which is much more convenient.