@Kat919 - I think one use for intermittent catheterization is for people who need a catheter because they can't empty their bladder, but who don't need to have a catheter in all the time. You can see how it would be inconvenient to have to carry around a bag of urine. (Though there are certainly people who do that, it's not one's first choice.)
I had a one-time catheterization when I was in labor. The baby was pressing funny and I couldn't empty my bladder, so they did a catheterization to get it out of the way. Later, I needed it again, but because of the risk of urinary tract infection they used a Foley catheter that time so that they could just put it in and be done with it. It looked like I was going to need an epidural anyway, and they usually use a Foley with that.