As its name implies, the AppData/Local/Temp folder contains temporary files. Those files contain temporary information while a process is creating other files. Normally, Windows deletes those files once the program closes.
Temporary files can recover lost information in case Windows or a program shuts down abnormally. In addition to .TMP, or temporary, files, the folder also contains other file types as well. In case those files remain in the folder even once the program shuts down, it is safe to delete them. If Windows does not delete the files after a reboot, this can be done either manually or with the help of cleaner software.