I was intrigued when I saw that Marshall Miles introduced "His System," which included an unbalanced diamond opening. I have used an unbalanced diamond opening for about 20 years, but not exactly what he describes. As the technique does have some "slam aspirational" benefits, and thus is perhaps relevant to this blog's theme, I thought I'd share.
Natural 5-card Major opening structures usually feature some variant as to "how many diamonds" if you open 1D. Maybe better minor, maybe 3 only if 4432, maybe 4+ (open 1♣ if 4432). I have seen 5+ as well.
My preference is 4+ if unbalanced, or 6+ (possibly with an exception if 2245/2254). This means any 4-4-4-1 (with diamonds), or 5 diamonds and 5431/5530/5440/5521, or 6+ diamonds. 1♣, then, will promise either (1) any balanced hand with at least two clubs (could, e.g., be 3352) or (2) any unbalanced hand with at least four clubs (same patterns as for 1D).
The obvious downside is that 1♣ is nebulous, although those who have used a nebulous 1D will know that a nebulous opening has some unexpected benefits (harder to make TOX when short in the other minor, picking off the opp's minor, less info for leads for the opponents, etc.).
The main benefit is that a 1D opening is sort of a min-splinter before the fit is found. A simple example. Your partner opens 1D and you respond 1♠. If the 1D opening was unbalanced, a 2♠ raise from partner will guarantee a stiff or void on the outside. As a stiff and a fit is worth about 3 points, the minimum opening range of maybe 11-14 now will be 14-17 by adding in the known shortness value. This makes game tries easier. BTW -- the relay should usually ask for the stiff, perhaps with a way to show min/max or 3-card/4-card support.
Note, that the ability to show the shape immediately allows Opener to not bid as aggressively. With a 16-17 count, because of the shortness value, you might ordinarily want to jump. As the 16-17 count is close to partner's expectations with an unbalanced diamond opening, however, you simply raise and trust partner to push when it matters. +110 is great also.
The obvious other benefit is in slam exploration. Knowing of the stiff immediately allows Responder to assess slam prospects at a lower level.
Some subtleties. 1D-P-1M-P-1NT is typically stiff in Responder's major and otherwise "balanced." Thus, 1D-P-1♥-P-1NT will almost assuredly be the auction for when Opener has 3154 pattern. This can help in minor slam exploration, and even with exploration of Opener's stiff suit. I mean, 1D-P-1♥-P-1NT-P-3♥ now shows a suit playable opposite a stiff.
There are many other inferential benefits to this approach. If anyone wants to discuss this more, feel free to email me.