Even for those without an easy, low/no cost MS liquidation method available to them, buying discounted or fee free VGCs and MCGCs can be a good way to maximize bonus categories or meet MSR by shifting spend.
Maximizing bonus categories - If you have a credit card that earns you a high bonus at supermarkets or office supply stores (e.g., the Amex Gold for 4x MR, BCP for 6% cash back, Hilton Surpass for 6x Hilton Honors points at supermarkets; or the CIC/Ink+ for 5x UR at office supply stores), then you’d use those cards to earn the high bonus multiplier on your VGC/MCGC purchases when these stores run one of these deals.
MSR - If you have to hit an MSR within a certain amount of time, you can buy VGC/MCGC and have the purchases possibly count towards your MSR. WARNING: Do not buy GC/VGC/MCGC at office supply stores with Amex cards while working on their MSR. At grocery stores should be fine as long as you throw in other items with your purchase.
Once you purchase the VGC/MCGC, you’ve shifted your spend in the sense that you made a purchase that you have to pay for, but you still have that money in the form of a VGC/MCGC. So if you’re doing this for the category bonus points, you made a purchase on your credit card that’ll get you the bonus multiplier (e.g., 4x MR or 5x UR) on your money, and shifted your money into the VGC/MCGC so that however or wherever you use up the VGC/MCGC you’re carrying over that bonus spend. If you’re doing this to meet MSR, you’ll have gotten whatever the earn rate was for the card you used at the supermarket or office supply store, and a purchase towards the MSR, but you’ve moved your money into the VGC/MCGC that you can spend at any time now or past the MSR period. (But it’s usually not advisable to be holding onto gift or prepaid cards for too long because they can be prone to hacking.)
If you have an easy liquidation method, you can use up the VGC/MCGC quickly and have the money back into a bank account to pay your credit card bill. If MS is not easily accessible to you, then you’re floating the money in VGC/MCGCs because you still have to pay your credit card bill for the purchases of those prepaid cards, but you’re likely then spending down those prepaid cards organically over a longer period of time.