As you have noticed, most of our work is done without the need to do routing manually, because Azure does that part for us, and creates default system routes in an Azure route table to allow the following:

• Traffic within the VNet
• Traffic between different VNets connected via the Azure VPN gateway
• Traffic between the VNet and the internet
• Traffic between the virtual network and other networks connected via Azure VPN gateway

So, you might wonder, can I do some customization other than the default system routes?

The answer is Absolutely, yes.

You can create your own routes between the networks to fulfill your scenarios.