Zelandakh, on 2014-September-13, 06:51, said:
The one-under DCB method is basically using 4♥ as Last Train. You can achieve the same effect by using Frivolous 3NT and normal Asking Bids without revealing the control situation when neither hand has serious slam interest.
I hate to disagree with you, but I think the first sentence is wrong. My understanding of last train is that its use neither denies nor shows that control, whereas the one-under denial definitely shows it. I see last train as useful in a situation where you do not want to or have not had the room to explore all the controls, sort of a serious NT at a higher level.
When you do have room, then the real advantage of one-under denial in the suit beneath trumps is a way of showing control without implying additional strength. You can still be a minimum for your pre-cue bidding. This in turn allows the partnership the use of cue bids in a co-operative slam try, where the initial cue bidder may be willing to go slam only if partner has a few extras that he has not been able to show yet. With this agreement, if partner is in this position of making the final cue and has that control, he can make it when minimum, allowing you to ace ask (or show aces) if super strong, but sign off if not. If he has it and has some extra value, he will respond with aces or ask himself. Conversely, if you (the initial cue bidder) are in the position of making the final one-under and have that control, you have the option of asking/telling aces when unilaterally asking, but making the final one-under to show it as as a co-operative suggestion confirming all controls.
Whether or not you view the benefits of discovering controls as more important than giving away information is a separate matter.
I do agree with the last sentence, and when partner is unlimited, 3NT as non-serious is arguably a better use of the bid. However, if partner has limited his hand, non-serious is no use to anyone, and one-under denial 3NT comes into its own.