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I allways had understood 1 ♥1 NT 4 ♥as strong and long and had never passed with the north hand. I cannot understand the sense in playing 1♥ 1 NT 4 ♥as a weaker hand, as I still can bid 3 Heart to invite pd....
With the hands strong in high cards, preserving bidding space is valuable for slam exploration. If you have a weaker freak, 8 hearts, or 7-4, you often do not want to bid 3H because that can be passed (partner will play you for only 6 hearts, perhaps more in high cards, 1-1.5 tricks less in playing strength). You want to bid game because on average it will still make opposite hands partner would pass 3H with. But you need to distinguish between the hands that are bidding game on extra distribution vs. the ones that are bidding game on extra high cards, particularly if you are playing 2/1 where the 1nt response has a higher upper limit and slam is possible opposite the jump shift hands. With the weaker distributional 4H bid, there is almost never slam opposite a 1nt response so the space isn't needed.
You are bidding 1h ... 4h on hands that you might have opened 4H with, but thought you were a bit too strong & might miss slam if partner had a 2/1 response. You aren't worried about missing slam opposite a 1nt response, but want to gamble on game, don't want to miss it by bidding only 3h.
There are better artificial methods available, but if your only agreement is "standard", you have to jump shift into a fragment (sometimes even a doubleton!) with one suited 18+hcp hands.