Carbonation drops are just premeasured doses of priming sugar. Sometimes they'll be a mix of glucose and sucrose, or just a single sugar depending on the brand. But otherwise they're exactly the same as priming sugar, so no chemical or taste difference.
They're probably being recommended by the instructions since they're pretty much impossible to mess up, which is great for new brewers since it's one less thing to worry about.
I had heard a rumor once that the drops that came with hopped extract kits like Coopers or Mr. Beer also had Maltodextrin, which increases body and head retention since extract kits often have deficiencies in those departments. However, I've never found any actual sources to back this up so it's probably just be overhearing the guy at a home-brew shop talking out of his butt.