Bouncing tracks in the digital world often means taking an "audio print" of a midi track.
For example, if you have a piano midi track, and want to play it back, then you have to either load the softsynth (which consumes resources) or have to attach the MIDI module or keyboard that actually produces the sound (which can be a pain, since you may not be able to carry the device with you everywhere).
If you know that the track isn't going to change, then you can cause the midi track to trigger the synth to produce sound, which you then record as an audio track. After that, you can disable the MIDI track and work only with the audio track, which can be more convenient and less resource consuming.
However, don't throw away the MIDI track! Just disable it for now - you may want to make changes again later, or use another synth to record its audio.