Okay - this is my career so I will tell you that the reason we need vitamins (and minerals, and amino acids and phytonutrients and trace elements...) is that our soils are depleted and our food supply drastically deficient. Next, you must understand that vitamin pills are generally formulated with a variety of ingredients, including inactive binders/fillers as well as waxes or even shellac that lets them pop out of the molds in which they are formed. Most are absorbed 20-25% which means that the rest of the pill passes through your digestive system and leaves your body. Read any of the extensive news reports on municipal sewage treatment plants, water supplies, etc., or talk to any septic pumping companies. Those undigested pills clog filters and work their way into our water supply. That's why some pills say to take on an empty stomach - to help them dissolve. But some are made with so many fillers and coatings that they upset people's stomachs - so the manufacturers cover their butts by saying "take with food". They don't really care if you get well - they just care that you don't get a bellyache or nausea which would cause you to stop buying their product. And most of them don't manufacture their own products anyway - they outsource it to another place (in another country with fewer standards, often) and then slap their own label on it. That's why so many pills from different companies look the same!
Nature intended for us to get our nutrients in conjunction with each other. Most vitamins, for example, need other vitamins to help them function. So piecing together individual vitamin pills can leave you dangerously deficient, and ask them to do a job they cannot do without their nutritional partners. Moreover, a lot of individual pills in the stomach can cause tremendous stomach distress. A lot of gastrointestinal problems are caused by a big pile of pills sitting in the stomach. Take a couple of your individual vitamins and put each in a small bowl of white vinegar - anything that's left undissolved after 20 minutes is what your stomach would not absorb and is therefore wasted money and unavailable nutrients for your system!
More than 3/4 of the US population uses supplements, yet a full 75% of us are nutrient-deficient. And we have record, epidemic rates of preventable, diet-related diseases!! How can that be? Because the nutrient levels are based on minimums set in World War II, and not optimal levels. Because the vitamins/minerals are not in a form accessible to the body. Because people play "kitchen chemist" and try to pick what vitamins they think they need. Because our medical schools don't require our doctors to take any nutrition courses or any food science seminars.
Cutting edge food science (supported by many years of research) indicates that a fully balanced, powder supplement that is mixed with liquid just before taking it, with the most bioavailable forms of each nutrient, can be absorbed and be working at the cellular level in 20 minutes. That means the nutrition is able to get through the cell walls, support mitochondrial function (the "furnace" that powers each cell to do its assigned "job"), and help that cell to flourish so that, when it divides, it creates 2 new healthy cells rather than damaged ones. If manufactured properly, things don't "bind" with other elements (as one post suggested).
In general, you need rapidly-available fuel during the most active parts of your day. For cell repair and ONLY for cell repair, a nighttime regimen is better. But unless you know what you are taking, you can't make that decision. Unless you get a degree in food science, you can't make that decision.
I've found that the best thing it to find a cutting edge company with incontrovertible research that bases all its decisions on clinical data, not commercial gain. Do they have a scientific advisory board? Are they part of the Council for Responsible Nutrition? Do they have a track record for humanitarian aid with their products and the resulting reports from the field showing that their products truly nourish? Do they offer a guarantee? Do they offer customer support on a regular basis, or do they just put their products on a store shelf and spend their money on commercials and celebrity endorsements rather than research? How did they perform in their last surprise FDA inspection? Do their products carry warning labels (like "keep out of reach of children")? Have they ever been sued or had a legal claim? Has anyone died or gone to the hospital from an overdose? You can eliminate 99% of the vendors out there based on most of these questions!!
Happy to help more if you are interested.