if you get suppressed normally you cant move and he will switch targets, with this way if he switches target you will send the hit-the-dirt squad mobile and walk straight through the machine gun
god has given you the ability to do human wave tactics, and you shall utilize them if you are audacious
To be honest I am not sure how long the delay was until you can de-activate the hit the dirt ability (haven't used it in ages) or if it still exists in the first place.
The way I see it, there are two options after immobilizing your frontal squad (suppression, hit the dirt), assuming players with decent micro:
1. Your flanking squad runs past the cone of fire. This forces the MG to retreat or reposition.
2. Your flanking squad gets suppressed as well. Without HTD, you can just retreat at this point. With HTD, your mobilize your frontal squad again. However you're in the middle of the cone at realistically range 30-40. You're not going to overrun the MG. Best case is that you can pull back one squad. With an half-decent opponent that switches targets, he will switch back to the frontal and this one gets suppressed, too.
The only gain I can see is that you can reactivate your squad unsuppressed if the flanking succeeded and the MG retreats. If there are other enemy squads in the area, you can fight them quicker. If there are not enough enemies to fire at the frontal squad to keep suppression, well, you did not gain much because the suppressed frontal squad will lose suppression quickly anyway.
Put you pay higher micro tax. You need to HTD at the same time your flanking squad should already ooraah around the MG.
Anyway, the whole point when this discussion started was about a defensive setup. HTD does not help at all. It's an ability for an offensive assault squad that needs to be close range. Your trade off is to not get a seventh man. 7 men Cons in green cover will at least decently damage an MG when shooting back. HTD PPsH squads will do even less damage, plus you make yourself vulnerable to nades of assaulting squads.