A good time to hit these targets is when your team is primarily conducting a push into the zones in which these targets reside and supply. For example, if your team is taking to the offensive in a zone (the best defense is a good offense), most likely they're going to knock out all the troops at bases within a reasonable coverage around the operational area. The starting ticker for these barracks (troops) is 2 hours. Rarely, if ever do I see a barracks stay down that long due to scripted resupply and manual resupply.
Obviously the ways to cut some supply would to go out goon hunting (or M3 hunting in the case of GVs) and targeting the scripted supply routes. The bombing alternate would be to bomb these strategic targets that are relative to the type of supply (Training Facility for troops, IE), and I think the magic % is below 50. Once below 50% operational, the facility takes a longer to start shipping out those relative supplies to a field within the zone. It's worth it when your team is pushing into enemy territory and trying to keep all the fields porked simultaneously and you don't own the "Home" field in that zone that controls all of the facilities that supply the various things. Usually bombers are tied up busy making sure troops, ords, dar, and FHs, and VHs are down at various fields. And usually the big coordinated raids go towards, you guessed it, the HQ.
The only time I've seen this in practice was one time my team was attacking one field on a lone island that was shared by another field that we currently owned. In the middle of the island was a Troop training facility (which we didn't control, as the field we had wasn't the "mother" field of the zone) which we got down to roughly 45%. Between that, and keeping tabs on the opposing field, we had to take action to make sure the troops were down less often. It's like a "behind the scenes" way of helping with the strat process. Taking down the troops at a field, and then hitting the facility for that zone below its optimal operational percentage, and that makes for one nice buffer. Then of course there's another huge aspect of hitting Cities so their resupply to the factories takes longer to keep their operational percentage lower longer, and then it takes even longer to fire off the scripted resupply routes.
It's a big net. The cities provide the factories and the HQ supplies, the factories provide the fields in that zone, and then the fields are the direct output for the players with troops, ammo, and fuel. As I see it, the progression (you could also reverse it, but doesn't make much sense to me) is hit the field strats, hit the factories if you can, and then aim for the cities. Of course, this would require a lot of manpower and/or decently, orchestrated, timed coordination to seem successful on certain levels. Mainly, hitting the strats with the most immediate effect is what chimes in.
But that's my .02. People might feel otherwise.
*EDIT* After writing all that, and seeing it written down.. it seems to be strategic bombing is highly overlooked and/or easily underrated in the effects it can cause if you have some decent, devoted bomber pilots besides the ones (or Jabos) already devoted to porking the fields.
