As Richard noted, you can delete recordings using the MBox (RED) key. However, there is no harm is leaving the recordings - they don't hurt anything and it's a circular buffer that will be overwritten after you have 1,000 recordings.
If you don't want recordings at all, you can turn them off with various settings in the PPS.
Ever since the phase II upgrade my G4 has been ending recordings silghtly early causing a word or two to be missing from the end of a transmission. I've tried turning triple buffering off however that did not fix anything. Is anyone else having this issue or heard of ways to fix it?