Pros: Use for multiple VFs per barracks. Delays tank rushes. Slightly slows resource drain. Cons: Vehicles don't build 'when you need them'. (I.e. Before VF goes down, rush is approaching, etc.) Players must wait in vehicle factory. Jeeps spawn faster. ( :p ) Also delay building other vehicles. Promotes boredom. Alternatives: Commander must approve all vehicles. Vehicles spawn with no armor.
Yeah, vehicles don't build when you need then, yeah people must wait, but this promotes strategy. You actually have to prepare you tanks for offence or for defence. Don't forget that the commander can still build tanks(not instantly) to prepare and players just need to hop in. In most rts, you have to make multiple barracks to spawn marines because each one tanks time. You have to prepare your army. Also, repair pads will be more prioritized. there will be more standard tanks alive that would prefer to recustomize because it takes longer to build new tank. Wuts wrong with faster jeeps?
At the expense of tactics, last ditch efforts, and fun. People just whine about jeeps because they can.