Be sure to try any tonic reasonably: take it regularly for at least two months. With some, you'll experience obvious effects, perhaps an increase. Exceptions to the general rule of using herbal medicines only when needed for a specific purpose are tonic herbs or adaptogens (traditional examples include ginseng and ashwagandha), which can help maintain a normal healing system, and Asian mushrooms, which promote immune health. With some, you'll experience obvious effects, perhaps a greater sense of well-being and more energy.
Or you may find that, over time, a tonic improves your response to physical and emotional stress and reduces your susceptibility to illness. Stopping taking supplements for a while can prevent dependence on them. It's not a big deal to follow a balanced diet to meet your nutritional needs. However, it's not really recommended, as the body needs vitamins and minerals to stay healthy.
It's more important that people don't suffer interruptions in their daily vitamin supplementation, especially if they take it to control a deficiency.