Russ shows the difference between Realtime and AudioSuite plug-ins in Pro Tools.

In the Pro Tools reference guide AudioSuite processing is described in this way.

AudioSuite plug-ins are used to render processing and modify audio files on disk. AudioSuite pro- cessing applies non-real-time, or rendered, audio processing to selected audio clips in your
Pro Tools session. Depending on how you config- ure an AudioSuite plug-in, it will either alter the original source audio file or create an entirely new audio source file.

Sometimes Realtime processing will be of benefit and at other times AudioSuite plug-in processing will be more suitable. Russ outlines the benefits of using one or the other.