If a file is still in use, trying to delete it won't work, "***.tmp is is use, delete failed" or words to the effect.
They are called temp files so that you or I know that deleting them is safe.
"Don't delete this file" as a name is trying to tell you something.
"this file is OK to delete" is saying the opposite.
The same is true for the contents of 'temp' folders.
If it was important, it would not have been 'given A name'/'put in a place' that means 'OK to delete'.
Temp files/folders are a PC's "rubbish bin". Sometimes the PC forgets to empty the rubbish. But if the PC put it in the bin, there is no need to worry about emptying it yourself. It's there for a reason, cos it's rubbish.