As I understand it, the "Temp" directory is use by Windows and other applications to store temporary data needed by either the O.S. or the app. When finished the O.S. and or the App, if the programmers that wrote the app were of any value, should delete the temp data.
The temporary I.E. files folder is a cache for web pages that you have visited. I don't know why Microsoft sets the default so high, but I have seen 2gb set for storage. This and other setting can be changed to decreace the size of the storage area, and supposedly delete the I.E. temp file when you close the browser.
If these are temp files I see no need to keep them longer than necessary.
bdj