Question: Is there ever a good reason to lead an ace against no trump when it isn’t top of a 3 card sequence?
Answer: Against suit contracts, it used to be normal to lead the king, from Ace-King. I found this confusing since the king was also led from King-Queen. Now, most players lead Ace from Ace-King. This has cleared up the confusion. For all other sequences, we lead the top card.
Against notrump, there are some special situations. One is to lead the Queen from KQ109 to ask partner to unblock the jack if he has it. Ace and King leads against notrump are special. The most popular method is to lead the Ace for Attitude (like from AKxx or AKx or AKJx), and the King for Count or Unblock (like from AKJ10 or AKJ10x). In other words, the King is the “BIG CARD.” It is easy to remember this using alliteration. In an auction of 1NT-3NT, opener’s hand may hold a missing Queen with at least a doubleton. By partner giving count, many times you will know how many cards opener has backing the Queen. You can drop a doubleton Queen or shift and partner knows to lead that suit whenever they gain the lead, or continue the suit, driving out the Queen when you have the known entry.
Some partnerships play Ace to ask for count and King to ask for attitude.
Others suggest that in a notrump contract, an opening lead of the ace shows a very good suit, and asks your partner to unblock by playing any honor he might have. Lacking an honour, your partner should give you a count signal instead of an attitude signal, since his attitude is irrelevant. Normally, you should have four of the top five honours with five card suit and three of the top four with a six-card suit. The lead of King asks for attitude. This is my preferred agreement.
Whatever agreement you adopt, make sure you and your your partner are in agreement as to what the Ace or King lead asks or shows against a notrump contract,