I think that it's like any other tool. Sure you could buy one hammer and do all kinds of work with it, but they do make tack hammers, framing hammers, sledge hammers, etc and they do certain specific jobs much better and more efficiently. Same with cars. You could both commute to the city and haul wood and concrete to the jobsite in an SUV, but perhaps a pickup would be better for hauling and a Honda Civic for commuting.
You could buy a nice, box stock AR-15 that could be used for precision target shooting, plinking, hunting and homeland defense. However you may be happier with your results with a specialized bolt action for target shooting, a 30 cal for hunting, a .22 for plinking, and a 12 Guage for Homeland Defense.
JMO