If you look at the Common Data Set for a school, it will show you if an Interview is Very Important, Important, Considered, Not Considered. For Yale for example, it is “considered”.
http://oir.yale.edu/sites/default/files/CDS2014_2015_5.pdf
You can google for potential interview questions and practice them ahead of time.
I think that is the most important consideration, as bopper pointed out. If the college considers it, you should do it.
I would strongly recommend taking the interview if offered. I was accepted to Yale w/o an interview, but I was also never offered one.
If they make the effort to reach out to you, oblige that! Effort is key.
I’m a little late to this party but I want to stress that Penn’s interview is very important but also very easy. Most of the interviewers are recent grads who just want to know if you are someone that they would have wanted as a classmate. You’ll be fine as long as you don’t do the following:
(1) Take 2+ weeks to schedule your interview
(2) Talk about your grades in an arrogant or condescending manner
(3) Answer questions with one-sentence answers
(4) Describe the Huntsman bathrooms as your visit to Penn
(5) Ask only questions unrelated to Penn, such as “does Philly have a mall?”
^