[JeffMorrow]

Recently, sitting second seat, my RHO opened 2♦. My distribution was 5=6=1=1. I bid 3♦ intending to show both majors. In the later autopsy, my partner asked whether it was standard to use Michael’s against preempts. I said I had no clue. Then I wondered if if it was not standard, why. Of course, one reason not to use it in this case was that I had longer hearts than spades, but my questions are general.

Is there a reason not to use Michael’s against preempts?

Should you use Michaels if you are 6/5 in the majors?

[P_Marlowe]

I think, the Michaels Cue is standard, although if it has to show the unbid Majors
or only spade + ? is a different question.
It is also quite common to play (Non-)Leaping Michaels, i.e. 4 in a minor showes
the minor and a (undisclosed) major, although (Non)Leaping Michaels is less common.

I think in the past, the cue was mainly played as Western Cue (?), basically a stopper ask,
but I think the Michaels Cue is now more mainstream.

If you are using the cue, you should have equal suit quality, because it is quite hard to
ask back, what is your better suit.
If you have 6 vs. 5, the 6 is a better suit, unless it lousy,
e.g. AKQxxx vs xxxxx introducing the 5 carder may not be good idea,
but AKQxx vs. xxxxxx introducing both ... why not.

[DavidKok]

Over here it is common to play 'Wereldconventie', which is the same as Leaping Michaels on this auction. It uses 4♦ to show both majors, and 4♣ to show 5(+)♣5(+)M with an undisclosed major suit. Both bids are forcing to game.

Traditionally the single cue bid (here: 3♦) shows a solid suit and asks partner for a stopper, to bid 3NT and cash 9 easy tricks. Over here it is increasingly popular to instead use this 3♦ as another two-suited bid, in this case showing both majors. However, this is definitely a nonstandard treatment.

[mw64ahw]

I had a similar situation recently when the bidding went:
1N 12-14-(P)-2♥ transfer

With no agreements I bid 2♠ having x5x5 and we ended in 3♣ for a top with others in 2♠.
Partner alerted but had no idea what I meant.

[pescetom]

We play 4♣ as clubs + major, 4♦ as majors and leave 3♦ as a stopper ask with a speculative 3NT, like the Dutch.
Over a Multi 2♦, 4♣ is unchanged but 4♦ becomes diamonds + major.