I think...yes and no.
I have to take potassium supplements because, for some reason. I am deficient in it. If I didn't take the supplements, I could go into heart failure. I was having terrible heart palps, racing heart episodes, and other things and had no idea why. All of my heart tests came back fine but I still had the symptoms. Finally it was discovered that I was deficient in potassium and have taken Rx supplements ever since, My heart is fine now. No more craziness. My levels are normal.
Same happened with Vitamin D. For some reason I was very deficient. I take 4000Iu a day by doctor's orders and I am now in the normal range.
However, mega dosing just to mega dose, I feel is wasteful and could be dangerous. People used to load up on vitamin E and it turns out it's dangerous at high levels. Several others have proven to be harmful. If a "normal" person took the amount of potassium I take, they could have heart issues. (Too much or too little affects the heart.)
I think a simple multi if you feel you don't eat well and, for women, a calcium supplement if you don't drink milk or eat dairy is plenty. I do strongly believe the multi should have Vitamin D in it - 1000Iu would be great but it's usually only 400IU.
Omega3 is also really beneficial for cholesterol levels and other things and we generally can't eat enough fish to get what we need. I take one gel cap a day and my cholesterol is normal. My entire family has very high cholesterol so I'm hoping to ward that off or delay it as long as possible and believe Omega3/Fish oil really helps. Again, my doctor told me to take it or I wouldn't have.
But I really don't believe that taking high priced supplements with many times the RDA is effective or healthy. Very few people eat so little that they are deficient in most vitamins and minerals. A blood test or two will tell you if you need anything to supplement your diet. I think that's the safest way to go. Or a simple multi and an Omega3 would probably be more than enough for more people to stay sufficient in vitamins and minerals.
I never notice a difference when I take vitamins and when I don't in my overall well being. Just the potassium which is VERY obvious when I am low.