Yes tansy does spread rather rapidly , but has great uses . I use mine all the time to keep bugs at bay. My patch is planted in the garden next to my bench. I pick fronds and crush them then slip one in my belt or hat while weeding ...works wonders. I also dry and then crush leaves to sprinkle about the garden when I see bug damage on my plants. About the only thing it does not repel are Japanese beetles.
I planted (from seed that I purchased) Tansy ~10 years ago. It spread very aggressively. It took me 5 years to get rid of it. However, I still have one pop up every now and then:)