It just depends on what sort of project it is. If you know that you will get millions of users per day starting from day 1, then you have to design for some lev

It just depends on what sort of project it is. If you know that you will get millions of users per day starting from day 1, then you have to design for some level of scale from the beginning. Prototypes in Python are common at Google, but usually it will have to be rewritten before launch.