For schools that require "at least 3" letters of recommendation for a grad school application, is it smart to send 4?
Personally, having one extra (a 4th) is probably not a bad idea.  However, there are risks involved.  First, just the logistics for interacting with 3 people for getting 3 recommendations is challenging enough.  If you add a 4th person to ask for a recommendation then your work may go up by a good amount.  Second, having a 4th raises the risk of having a negative statement from a recommendor that could hurt your chances.