Always mute the mic when switching between V or I modes to avoid hearing a loud POP. Switching the mode means you are simultaneously switching the input and output of the mic’s dual set of electronics!
For vocals or lower SPL sources, start with the "V" mode and use the proximity effect to taste. Bock’s V mode offers a classic vocal mic sound that’s "warmer" and not overly bright.
For kick drums and other high SPL sources, try the "I" mode. This classic FET sound may be used close up on a kick drum, snare drum, toms, bass amp, or super-loud vocalist.