I used to climb quite a bit. Also a fisherman (mostly saltwater, but flyfishing too). Hard to escape tying knots if you do either. Do you need a ton of knots? Probably not. But I enjoy knowing them and seeking uses for them.
On an aside, I find knots fascinating. It's the romantic as well as artist in me. Some knots are clumsy workhorses, others beautiful and elegant. The Siberian Hitch mentioned earlier is a beautifully simple work of art and design in my opinion. I like the mix of form and function involved.