Why yearly mammos when nothings there?

Last year I had a fibroadenoma and microcalcifications removed and was told that I now have to have yearly mammos. Most people I know have to have 3 yearly, even if they have had a lump removed. I have been told that all is clear and I am not complaining that they are keeping an eye on me, but I was told that there was nothing there. Im not sure what to expect in the future. Im not losing sleep over it I am just wondering. What would you think?

Yvonne x