I have had frogspawn in tank for 6 years and never fragged it, just made a huge colony.
Its up to you, you can kind of trim them to the form you want, but they will grow in areas of lighting that they find desirable.
I have never noticed fragging slowing down growth, I think that most of the heads operate as individual corals almost.
The only real reason to frag is if you want more, or are going to sell them. Never fragged my big one because its got really gross colors.
Cant bring myself to ditch one of my first corals though. That was probably closer to 8 years ago now.