Your body turns beta-carotene into vitamin A only as needed, which helps avoid the vitamin A toxicity possible with large doses of preformed A. It is a fat-soluble carotenoid, so take it alongside a meal that contains some fat for proper uptake.
People often use beta-carotene for eye health and immune function. No mainstream authority has set a tolerable upper intake level, though very high amounts can cause harmless skin yellowing called carotenodermia.
High-dose beta-carotene supplements have raised a clear concern: increased lung cancer risk in current smokers.