I bought Family Tree Maker specifically for the relationship calculator. That's how I found out my ex-husband's grandparents were 8th cousins, which I'm sure they didn't know. But I really wanted to know how many times I was related to Queen Elizabeth II and why I didn't get an invite to Kate and William's wedding!
What I don't like is that for some reason, I cannot see the relationship path in my other trees. I can see it in my primary tree, and it will update if I change the home person to my mom, or someone else. But my private, research trees? No relationship path comes up. So I have to use FTM if I want to see the different paths.