Do you need an audio interface with a Mac?
You only need an interface if you plan on recording external audio. You do not need an interface for low latency performance on a Mac. You generally do not need an interface for low latency performance on a PC as the free ASIO4ALL software creates low latency ASIO drivers for most built in audio on PCs.
Do you really need an audio interface?
Answer: Yes, you need an audio interface, even when you make beats or electronic music. The main reason is because of the audio quality which is needed for professional music production. This quality is lacking in most sound cards shipped in laptop and desktop computers.