Being new to 3D printing, I'm still learning the basics, including things that seem to be omitted from all the tutorials I've found online. One of these is what to do with filament between print sessions -- leave it in the printer or extract it, then re-insert it for the next session. If the latter, just how long can one safely leave filament inserted in the print head? (It can take several minutes to remove a print, clean up, etc., before starting a new print.) Thanks for any advice!