If it has the same relative safety of use as penicillin lines of antibiotics, but is more robust in its method of action to prevent resistance occurring as easily, then my guess would be it would be preferable to use as widely as possible.
The idea is that drug resistance comes with a metabolic cost. We're making them do something to survive that we didn't before, and it's going to come at a cost.
If we think of them like cars--armoured ones are extremely rare. However, if we started randomly shooting at cars, and did so for a protracted period, we would eventually see them become more common. The fact they're slower, don't turn as well, and use more fuel is now negligible because of the excessive benefit of it's contents not being shredded.
If the implementation of this new antibiotic came with a moratorium on the prescription of penicillin, then we would be targeting the population as a whole with an RPG. It doesn't matter if you're armoured against bullets anymore. Both the normal and the resistant will be put under the identical survival pressures, which should mean it is more effective against the resistant strains as these won't be as fast to replicate.
The problem from what I understand is that tackling antibiotic resistant drugs with drugs designed for antibiotic bacteria, just makes super bugs.
Essentially if we cleared the roads of regular cars and left ourselves with armoured cars, and then start firing RPGs at them, we'll end up with vehicles resistant to those. We will end up with APC's on the road.
If we implemented a moratorium on penicillin strain antibiotics, we could potentially reverse the current epidemic of multi-drug resistant strains. It would be like starting anew - assuming there's no genes that are equally beneficial against both drugs.
That's my understanding of the reasoning behind suggesting broad use, but I could be way off.