Questions about controllers

[genxbigboy]

I have been in the hobbies for about 10 years on and off. I heard of controllers but have no clue to what they are used for. On a 1-10 scale is it necessary or is it just a luxury item? Enlighten me please.

 

[karsseboom]

http://www.youtube.com/watch?v=ovFDR3lSYeg&feature=youtube_gdata_player