I would say that I haven't really seen any reason not to use Airwave - I'm managing 110 iAP clusters and 105 of them on the same template.
(I am so comfortable with the template that I've not tried very hard to use the GUI in Airwave)
The only issue I've seen is that the Airwave and iAP teams work at different pace and if you keep to the bleeding edge on both products, there are features in iAP which Airwave doesn't support yet, and occasionally Airwave has a feature which was impelemented slightly different in production on iAP.
If I was just managing three iAP clusters and had no other requirements of Airwave I might be tempted to skip Airwave - until I wanted some historical use/accounting data. Which the iAP doesn't have.