the process is very simple.
Make a photo of the subject with the card.
Convert only that photo to DNG and drag it into the software.
The software will create the profile.
That profile can be used on the normal RAWs (no need to convert to DNG).
I shoot a checkershot with every change in lightsetup.
In the past I used the gretag but stopped because it simply was too much work and switched to one profile per lightsetup and used whitebalance cards.
With the colorchecker I'm back to shooting a colorchecker before every serie.
The difference varies per lightsource, especially the 5DmkII benefits A LOT under studio lights, my Leaf Aptus does benefit but less dramatic.