The M2 is a large caliber MG. This may not be useful in certain anti-personnel applications for various reasons.
Indeed, and the M2 is very accurate which is great against the stationary and material targets it's meant for, but it also means its pretty much useless in its anti-personel role. The Bren had the same problem.
If you're fighting infantry, you might want a weapon that sprays bullets all over the place so you can hit several targets with one burst. Hence this modification I guess.