That IS the whole point. Chemo is hard enough as it is without worrying about them finding a good vein every time and veins do blow out over time. I have tiny little veins that roll and every time I have to get stuck for an IV it is difficult. for the nurse to find and often takes more than one try. I didn't have to worry about any of that when I had my port and was getting chemo.
There are really no downsides to a port that I can see except that, like other surgical sites, there is some risk of infection. I had surgery with general anesthesia when they put it in but taking it out only required local.

Nelie