I never realized how much of a difference a tie could make until I saw a man in a blue suit transform right before my eyes. He didn't look shabby without them, but the tie and pocket square added a wow factor and took his look to another level. I wish I had a picture to show you. But, the one to the right should do.
I suppose if you're going for a more casual look, sporting a suit sans a tie and/or pocket square could be appropriate, but to dress it up or even change the look of a suit you've worn one too many times, these subtle additions will definitely do the trick.
However, you can't just add any old tie. The tie and pocket square should make the suit come to life (see image). Notice, the tie is not the same color as the suit, but it adds a nice contrast and feel without taking away from its flare. It's also nice when a tie makes the suit pop by adding a much needed spot of color if you're wearing a simple black or blue suit.
If you still need more reasons to add a tie, there's nothing more alluring than a man donning an undone bow tie or loosened necktie at the end of a long evening. It's definitely right up there with the 5 o' clock shadow or a salt and pepper beard in terms of sexiness.