I am planning to install 15-18 recessed lights in soffits in a couple of rooms in my house. I plan to run two new 20 amp circuits from a subpanel (capacity is fine? and divide the lights half and half. Judging from some of the other posts there are reasons to use 15 amp circuits instead. If I am going to the trouble of installing new circuits why would I not want them to be 20 amp for future expansion? Thanks.