Vitamins are "vital" substances that the body cannot make itself and need to be added from the outside through diet or supplementation. So if your "being the kind of person who takes vitamins" means that you eat an extremely balanced diet that covers all your macros, then you are good, but most people do not eat enough of the right foods.

In addition, there are tons of substances that your body can synthesize itself, but would love more of it. Creatine for example can be made in the liver and kidney from L-arginine, glycine, and L-methioninein, but it takes work for your body to do it. It is much more efficient (something like 20X) to just take a creatine supplement and bring it to levels that will allow your body to maximize it's production of the energy molecule ATP (by resupplying a phosphate molecule).