NOSB is amazing if used at the same time as DP-28 Stand Ground because the movement modifier is already in place. However, the best use is on conscripts because their losses are very cheap and you can let them do some significant damage which they wouldn't normally do. It's also very useful to use it if you manage to get past an enemy MG and you can pop NOSB while behind the lines. This is risky if your forces are weaker and you could lose squads due to slow movement but you can also deal a devastating blow. If you need to, you can also use NOSB on a few squads fighting an MG front on. They should defeat it.
The easiest and most logical choice is to use NOSB on whatever is defending your OBR cannon when the enemy tries to rush it. A well placed OBR is not something you want to lose to an enemy push.