To answer your question, no you don't
need an interface, unless you need more audio ins/outs than just stereo out from your macbook.
Latency-wise, Apple's CoreAudio has been and continues to be fantastic. All third-party developers essentially build on top of CoreAudio, which is why you'll often see their driver type as... well, CoreAudio!
So an audio interface frankly won't make much of a difference there, if any. If you were on Windows, that could be a different story.. (maybe that too has improved, who knows)
For context, I used to perform electronic music with a bunch of midi controllers and Ableton. Live glitch/mashup/controllerism, so low latency was a must. For years I ran straight out of my MBPs headphone jack into mixers. Only when I started jamming with other musicians / live looping I had to go with external IO. Made no difference to cpu/latency, same as before. Only real noticeable change was the extra thing I had to lug around in my bag.
Keep it simple, save yourself some money, be happy.