I presume you are talking K, L, and N Frame Guns.
If you conceal carry, a round butt with a compact grip does not print as badly as a square butt. It will also be more compact.
If your gun has a round butt grip frame you can use either a Round Butt Grip, or a Round to Square Conversion Grip. You cannot go from Square Grip Frame to Round without a Gunsmith altering your grip frame. Not recommended on anything that might ever have collectors value.
I have an assortment of both Round & Square butt guns.
I like round butt compact finger groove grips for my concealed carry guns.
I tend to like Square Butt grips more for my larger 4" barrel Range & Field Carry guns. I prefer Square Butt for heavy recoiling guns also.
Bob