That is, the magazine is outside the grip frame, usually in front of the trigger guard. Maybe somewhat bulkier to carry but people with smaller hands could use bigger calibers with less difficulty. And yes, I know the original Assault Weapon Ban listed that as one of the characteristics of an eeevil assault weapon, but except for submachine guns or semi- versions of same, they’ve never been common.
Reloading a magazine in the grip is easier, as you’re moving one hand to another. If the magazine well is in front, you don’t have that coordination.
More expensive. You have an extra 2 1/2 inches of receiver, and a shorter barrel.
Not compact. In fact, the Mauser often didn’t come with a holster but rather a carrying case that doubled as a detachable shoulder stock.
Clumsy reloading, as mentioned above.
But then, you do have more modern firearms like that. There was a Hi-standard .22 target pistol. Then there’s the pistolized version of the .223 Bushmaster. It has its advantages.
To add to the examples, the closest modern equivalent is probably the Tec9.
I figured you were talking about the Mauser C96, but it’s worth mentioning Mauser did make another fairly successful semi-auto handgun too - the Mauser HSc.
The original C96 models were reloaded by charger clips, which is, well, a bit clunky - even if you know what you’re doing.
Also, you’ve got all the weight of the magazine (and a magazine full of 7.63x25mm or 9mm Paraballum rounds is not especially light) in front of the grip, which can affect the gun’s handling (not significantly - I mean, after all, a revolver’s cylinder is forward of the grip too)
As has been mentioned, there’s quite a few target pistols with the magazine in front of the grip as well.
The C96 is something of an outlier in that it’s one of the very few successful commercial handguns where the magazine isn’t in the grip - even really early designs like the Borchardt C93, the Steyr-Mannlicher M1894 and the FN M1900 all had the magazine in the grip.
Lumpy–tell the truth.
You want us to bring you the gun of Han Solo*, doncha? 
*“Lord of War” ref. Yes, my jokes are footnoted: this is the SDMB, after all.
Actually I was thinking about Karrin Murphy, the Badass Normal of the Dresden Files stories. Being all of five-foot nothing, she could use a custom gun built to shoot .50AE if she didn’t have to deal with a hugely thick grip.