I do this when the game is already well advanced. For example, I recently sttled in Palermo in GW3, and for a line that needs 4 E190 to be fully served(and with no opposition), I just drop a E190 qith 4 daily flights there, a marketing campaign, and I'm forgetting it. I'm gonna lose some money, but I don't care. itÚs easier like that
OTOH, when the game begins and you are not rich, it's better to take the time of building a broader network of unfilled destinations. It's more work, but profit comes quicker. And that's the alpha & omega of early game : get as much profit as quickly as possible to fuel your growth.