Hi,
TG2 does save files to the temporary items folder, mainly after finishing a render. Normally it will save the image and the alpha buffer for the image. This can be handy if you have a crash during rendering, sometimes you can retrieve something usable from the file save in the temp folder.
To be honest, I'm not sure why it is set up by default to always save the alpha image.
Further to that, I'm not 100% sure what the policy is regarding deleting temp files on the Mac. The oldest files I have in the temporary items folder are just a couple of weeks old and I haven't deleted them manually. Looking in the Trash I do see some TG2 temporary items which are about 3 weeks old (haven't emptied the Trash in a long time :-). It looks like the OS might be cleaning things up every couple of weeks. Of course it doesn't take long for these files to take up a bit of space, especially if you are rendering a lot of large images. However I reboot my machines sometimes several times a day so if you tend to leave yours on for long periods that might make a difference, as I believe the temporary items folder gets cleaned up during startup.
I'll discuss our temporary files policies with the others. It isn't something we've taken a look at in a long time and perhaps we need to reassess why we do things the way we do.
If you want to check out what temporary files have been created by TG2 you can select "Reveal Temporary Files" from the File menu.
Regards,
Jo