The reference to entries on yesterday's hand reminded me of another hand, some years back, where entries became of paramount importance. It was rather amusing to me because I saw it played twice, though not by design, and each declarer made the same mistake. I had dropped into the club late one evening, sat down to kibitz a friend, and watched this hand being played. Then during the changeover, I realized I was in a traffic pattern and so skeddled to a side room and found myself looking at the same hand being played. Actually, one declarer was in 6 hearts, the other in 6 no, but each got the same opening lead, and each went up with the queen of spades to take it. The queen of spades!
Now each led the queen of hearts. It looks like a cakewalk, doesn't it? You knock out the ace of hearts and everything's solid. Except that hearts are 5-0, and declarer is an entry short of picking up the heart suit on a double finesse. Well, okay, one could manufacture an entry by way of the 10 of diamonds, but neither one did. [Actually, West could foil that plan by going up with the J. But it's absurd to think that anyone who was so careless about his entries on the spade lead would attempt that.]
East takes the queen of hearts with the ace and gets out with anything but a heart. Declarer later goes to the ace of diamonds and leads a heart, but East splits his 9 8 and declarer must eventually lose a second heart.
One would hardly have supposed hearts would split 5-0. No. But what's the point of going up with the Q of spades and leading the Q of hearts? Look at it this way: you have a minimum of seven entries to the South hand from North, but only two sure entries going North. And you can always lead toward the Q of hearts. So why chew up one of only two certain entries to dummy in order to lead an honor you can lead toward? It's not as if you needed to take a trump finesse at trick 2. Then there would be some justification for spending that Q of spades entry. But here?
With that disparity, don't you think you'd like keep one of those two entries to dummy till later, making it 2 entries one way vs. 6 the other, rather than 1 to 7? Or to take spades alone, wouldn't you rather be able to go to either hand at the end of trick one rather than being able only to travel South? I'm not going to lay down any absolute rule about preserving entries in the hand with the shortest number. If I did, someone would be sure to shoot it down with a surprise on some hand. And certainly, however short the number, if you need to use up a scarce entry in one hand -- say declarer had the ace of hearts instead of the king and wanted to take the hook -- then I guess you'd better use it and get on with your business.
Nevertheless, I would suggest that unless you can envision otherwise, when there is a marked disparity in entries to one hand or the other (not a difference of one or two), you'd almost certainly do well to eat up an entry to the hand with the most and keep as much communication in each direction as possible. Here, you don't need to lead the queen of hearts when you can lead toward it just as easily, and when the unexpected split was revealed, it sure would be nice to have two entries to that other hand. Indeed, that queen of spades entry is what makes the slam (as opposed to A K tight in spades and A K low in clubs, which would give you the same number of black-suit winners but not the same number of entries).
In any event, you'll note that if you keep the Q of spades, a lead to the Q of hearts reveals the split. Whatever East leads after winning with the A, you go to the Q of spades, lead a heart, and East must split his 9 8 to prevent your running the hearts. Okay. Just go back to the ace of diamonds, and now a third heart lead picks up the suit. Bid and made.
Q 6 5
Q 7 5 
A 10 6 3
10 7 3