Doubling is a fine technique to use if it helps you accomplish the sound you are looking for!

I have used it on vocal tracks to "thicken" my voice. And I have used it when I want a background of something like a strummed acoustic panned both right and left.

Of course you have to do a little more than just double the track...mainly add some delay to the doubled track. Check out these articles for more info,

https://www.soundonsound.com/sos/apr09/articles/doubletracking.htm

http://music.tutsplus.com/tutorials/how-to-create-rich-depth-with-doubling-techniques--audio-559

Oh and John Lennon famously used Automatic Double Tracking to great effect!