A clicker is just another marker that you condition the dog to mean he did something right and rewards are coming. Theoretically, a dog can be conditioned to anything from a click, to a clap, to a word.
There is research that suggests that the sound the clicker makes bypasses something or other in the brain and thus is more direct to the reward center in the dog. Take this with a grain of salt and do your research because I will not find any sort of proof to back up my claims but it's something I remember reading about.
With that said, I think it comes down to personal preference. I never used a clicker but instead conditioned my dog that the word "Ok" means a release and reward is coming. I just find that when using balls or tugs as rewards the clicker gets in my way and I dont always have it with me (but I always have my voice).
This is just _my_ opinion. I was able to get pretty complex behaviors out of my dog without the clicker so it can be done with or without.
In the end it's what feels most comfortable for you.
Also remember, clicker or no clicker in the end its all about your timing