During a registration process what would the reasons be for using: username/password or email/password combinations to register the user?


Is it a case of identification once in the system (may be preferable
to refer to a user by their username instead of their email)
Simplicity - using email means the user dont have to create two
memorable items?


What other reasons are there for choosing either option? Is there a relationship between the type of service? 


Question: Easiest way to create a binary variable
Answer: Boole@Thread[Greater[x, y]] ==  MapThread[Boole@Greater@## &amp;, {x, y}]