Adam, the type of catheter we are talking about is a Folley type baloon catheter. It is inserted, then a baloon is inflated at the tip (inside the bladder). The catheter stays in place for up to a month, before being changed out.
We ONLY EVER have these inserted per our doctors recommendations, and under their guidance. Most often, it is called for when our sphincters are not working, our bladder are distended to overflowing and need to be shurnk/rested, or (like me) we have a urethral blockage.
With a folley cath in place, this allows our bladders to constantly drip drain. Normally, the catheter is hooked up to a collection bag, but many (including myself) find the bags to be cumbersome and uncomfortable- especially when more than a cup or two of pee is weighing it down to one side.
Since diapers are contour fitted, and spread that pee around, they are inherently more comfortable. There used to be an old concern that an open catheter system will increase a chance for UTIs, but urologist have come to realize that as long as we are constantly dripping pee, we are constantly flushing it out- and not giving any bacteria the chance to take hold. Staying well hydrated is extremely important to ensure this too.
As a side note, all diapers tend to work better when we have a constant drip, versus flooding them all at once. This allows the diaper more time to wick the pee to other areas without overflowing and leaking.
It also tends to be more difficult for us to notice when the diaper is full too (since our pee is better wicked away without building up). As such, high capacity diapers like your Supremes or Betterdry (or Confidry too) are always a must when letting a catheter to drip drain into one.