@mesch is correct but be aware
1) Changing VTA changes VTF so you are hearing two things at once, and if you are making a large change to VTA then VTF will have changed substantially which is presumably not something you want
2) Unless you have an incredibly steady hand and a non suspended turntable you risk damaging your cartridge if something slips as you make the adjustment
So in my experience VTA adjustments should be done carefully and incrementally and rarely "on the fly" (Kuzma and others offer remote control adjustment which obviates #2 but still problem #1 applies)
Azimuth may be the exception but few tonearms allow this to be adjusted on the fly (my Kairos is one that does but even so caveat #2 above rules out my trying to do this)
Your question has been more or less answered but I wanted to add that typically you would adjust tonearm height to compensate for different thicknesses of records. Record thicknesses can range from 0.85 mm to over 2.15 mm and being able to adjust tonearm height keeps the stylus at a fairly uniform VTA/SRA and corresponding VTF. Small adjustments in height can be made to compensate for differences in SRA of the cutting head when the master disc is made.
Most tonearms do not allow for quick and easy height adjustment, let alone "on-the-fly" height adjustments, so a common solution to accommodating different record thicknesses is to use platter mats of different thicknesses. Quickly swapping or layering platter mats provides a way to maintain a reasonably consistent VTA/SRA and VTF.
For example, I set my cartridge to have the desired SRA and VTF for a 2.00 mm record and use a combination of three platter mats to keep the height at +/- 2 mm. (A chart showing the combinations is found here: http://gallery.audioasylum.com/cgi/wi.mpl?u=32746&f=plattermatstoadjustsra.jpg&w=412&h=7...)
But a single 0.8 or 0.7 mm platter mat could be used to raise the height of most records (typically 1.0 to 1.1 mm thick) to the common thickness of heavyweight LPs, which is 1.8 mm. It’s not ideal, but it at least accommodates for the majority of your records and lets your "audiophile" LPs sound their best.
I've found that the Herbie's Donut mats I use can actually sound better than a bare platter with thinner LPs because they reduce resonance vibrations (distortion) and especially because the mats maintain correct SRA when using micro-line and micro-ridge LOMC cartridges, which seem to be more sensitive to SRA. The heavyweight LPs are used without a mat.
Occasionally having to swap mats to accommodate different LP thicknesses takes all of 10 to 15 seconds of additional time. For me it's worth the effort. (Consider that most of my LPs are 1.0 to 1.1 mm thick and use the same mats so I don't change mats that often.)