Add multiple API Keys or Sub API Keys to be used for commercial software distribution.
I have some software nearing completion and it will be distributed to customers on a subscription basis. A few customers would also like the host the software themselves. Maintaining multiple API Keys that link to the one account allows us to control our customer's usage should the subscription expire and prevent us from giving them our API key.
Liam O'Boyle commented
Or even if you have multiple applications using one mailgun account. I was very surprised to see that I could only have one set of secrets.