Why are covered calls bad?

Can you explain why some investors view covered calls as a potentially unfavorable strategy? Are there specific risks or drawbacks associated with this approach that should be considered? Perhaps we can discuss how the sale of call options against one's holdings can limit potential upside gains while also potentially exposing the investor to downside risk if the underlying asset's price falls significantly. Additionally, is there a time or market condition when a covered call strategy might not be advisable?