
Perhaps you need to fall back from combat and the officer nearby died in the assault, so now another officer down the line can order them to get back in the fight. It's nice if you have very tall buildings or terrain to order guys 6" up a building but normally if they're going to need orders you just put an officer up there with them. Outside of these specific examples, Voxes are kind of situational and usually only brought to look cool or because you have the models. Voxes let you use "Superior tactical Training" to order units outside of 6" and let your "free" orders affect units within 6", letting officers like Creed or a Master of Command Commander to order a whole platoon around without them having to be bunched up. Without Voxes, they require you to bunch your army up into a little murder ball that assault units just love to get mixed up in. Cadians have a few different ways to spam a stupid amount of orders. The second, and more specific example, is Cadians.

This also works for vets that are outflankers or riding up the field in transports although again, normally you'd just bring another officer. This way if your two squads who need orders are on opposite sides of the board, you can still give them orders. In this case you only have a couple of officers and so to deal with the fact they can't be everywhere at once, Voxes let them order wherever it is needed or hide out of the line of fire should your opponent have snipers.

The first would be you have a very limited pool of officers due to slot constraints, like some odd ball tournaments that limit your slots or leagues just starting up. Usually you're better off just buying more officers. For reference, 4 vox casters buys you a platoon commander, 6 buys you a company commander.
