Most reef tanks don’t need to have elements dosed. Most premium salt mixes replenish calcium and alkalinity and minor elements that corals and coralline algae need to grow and thrive. The exception to this is SPS corals. Small-Polyp Stony corals are much more demanding and will need calcium and alkalinity and magnesium, and other trace elements dosed to ensure they thrive.
It will take 12-18 months before this becomes necessary for most reef tanks with a large amount of SPS coral. SPS frags and smaller corals will generally grow well, initially pulling the elements they need from the elements in premium salt mixes. Once they get bigger, it’s time to consider supplementing elements, or your SPS corals will begin to suffer.