One might prefer to have more to hold on to, more to strap a light to, or more magazine capacity in a gun that operates reliably with at full-size magazine. I've read a number of comments regarding the challenge of getting the 1911 design to function reliably with 3" barrels, and my own experience has not been good with G20 magazines in the G29.
Now, magazine capacity isn't a factor to me--so that's no reason to get to a full size gun for say, home defense. But, if I have a gun I can get both hands on in a hurry off the nightstand, leave the light on it and not have a light on my carry gun, I'm a little happier.
I do believe that for most folks, the smaller the gun, the more difficult to manage. But the intermediate-sized guns, for example the M&P 45 Compact, are, IMO, not too small and not too big. They really do serve well as both cc and hd guns. At least for me.
Also, I may not choose to carry a 45, perhaps because I want lots of capacity and simply want a smaller package. But for home defense, it may be I simply prefer to have something like the 45 AND some capacity, but don't want to step up to the shotgun as my primary nightstand gun.
There's simply the issue of perception and preference, too. I think there are lots of folks who don't accept that little guns do as well as big ones, that little calibers are as good as big ones, etc. Facts, alleged facts, hearsay and statistics don't override just 'feeling better' about what you're going to use to save your skin.
I prefer my Glock 29 to my Glock 20 in all circumstances, and prefer my MP45c to any 45 I've ever fired. But, I don't think of these as 'sub' compacts--they're right-sized. I personally don't see any purpose for a full-size version of these guns. Since I already have the G20, it does duty for hd when I'm not carrying in the house (bedtime). I wouldn't (and didn't) buy it specifically for that purpose tho.
