This example is from Victor Mollo's "Test Your Defense, Where the Points are Won."
You are East. The bidding has been 1NT pass 3NT pass. West leads what looks to be the fourth highest spade. You hold:
(s) Axx (H) KQJ9 (d) Kx (c) xxxx.
Dummy shows (s) Kxx (h) Txx (d) Axxx (c) Kxx.
You take the ace of spades. Normally you would return a spade, partner's suit. But Mollo recommends establishing the hearts for a "set."
The key features are: 1) Dummy's T falls under your J, making the 9 good 2) you have the guarded K of diamonds "offside" the ace, hence a sure entry and 3) You have 13 of your partnerhip's HCP. West has the J of spades at most (Q if South has only 15 HCP).
So is your strength the reason you should deviate from the usual rule of returning partner's suit? Should you return your partner's suit if you didn't have the heart honors (meaning that partner has about 7 HCP), or if you had only the A of spades (partner has about 10)?
Conversely, if you were "West" (on lead), would you lead differently with the three different hypothetical hands?