Empowered buildings will build, research and train 10% faster. Additionally, empowered dropoff buildings (Town Center/Storehouse/Dock) will cause more resources to be generated (a villager returning with 10 units of food will actually put 11 units of food in to your supplies. The actual number will depend on the Empower Dropoff stat of your Priestess of Ra).
It's important to have your Priestess of Ra in a separate control group during a battle, since they will not heal nearby allied units if given an Attack Move order.
Always have a Priestess of Ra on your Town Centres - Egyptian villagers have a base train time of 18 seconds compared to the 15 of other civilisations.
The Priestess of Ra is considered a military unit. Easy Drag Military will still select the Preistess as well as move/select all military units.