Well, nothing really—if a service offers two-step or two-factor, you should absolutely enable it, and it’s not like a service will give you a choice between the two.

A multi-factor model uses many factors in its computations to explain market phenomena and/or equilibrium asset prices.

Revise, multiples and factors, prime, square and cube numbers, the product of prime factors, and powers and roots with this GCSE maths guide.