Thanks for replying!

 

But 

"A developer license entitles a single developer to install and use the product on ONE machine."

how "Developer license benefits a single developer with many sites"?

 

 if I buy 1  developer license can I install on 20 domains of 20 different machines I developed?

 If yes, then I understand the benefit of developer license.

If no,  can you show me a case where developer license is better than other options?

I can think of a case where I have one physical machine but running 20 domains of 20 different IPs,

is this the only case where developer license make sense?