Rationalizing the denominator has been a regular part of Algebra 2 since forever.   I learned it and still teach it.  It is an important trigonometry skill. 

a/sqrt(b)

a/(c+sqrt(b))

(a+bi)/(c+di)

The main importance, in my opinion, that numbers that look different are can actually be equal.  1/(sqrt(2)-1) = sqrt(2)+1 for example.  So having an agreed upon format for the answer is a good thing.

It's not unlike working with reducing fractions in the lower grades.  

Of course, if the expression in the problem came up while working on some other problem, I would leave it alone!