The advantage is bragging about a bigger gun... thats about it. I have a couple of 'magnums' but I primarily hunt with a 25/06. It does everything I need and its still very flat shooting
Begging your pardon Matt, (and to dispel the notion that a "magnum" is something with a belt to headspace on, instead of a shoulder or rim) but...the 25-'06 IS a magnum! If we can set aside the terminology and analyze what makes one cartridge a standard round and another a magnum, I think we'll agree that it comes down to case capacity versus bore diameter. The presence of a belt, or the word "magnum" in the naming of a cartridge, does not a magnum, make. Rather, it is any cartridge which, for its given caliber, offers more case capacity and higher velocity than others in that specific caliber.
A 30 Carbine, 300 Savage, 30/30 Winchester, 30/40 Krag and 30-'06, etc...are all .308 caliber rounds that are not magnums. By comparison, the capacity and velocity provided by the 300WM, 300WSM, 300RUM, (and on and on) are magnum rounds because they offer quite a bit more in terms of power and long-range performance. One of the first 30 caliber magnums was the 300 H&H, which had the belt, but the 30 Newton, with comparable ballistics, did not. Both were, and are, magnums, not by virtue of their case design, but by their capacity.
To further illustrate that a magnum need not be labeled as such, the 220 Swift is, by all accounts, a 22 caliber magnum. On the other hand, the 222 Remington Magnum is perhaps misnamed as there are several other 22's that exceed its performance and it is only a "magnum" by comparison to the original triple deuce.
So, if you want your bullet, of any given caliber, to go a little faster, hit a little harder, and drop a little less than most offerings in that particular caliber, then get a magnum. If not, don't worry about tags and labels and just shoot what you know will do the job you have in mind.