Temporary files are usually generated by software for one of two reasons; either as a backup file or as a cache. In the case of cache files these can be generated automatically by programs that run out of memory space to allocate for tasks.
Most of the time .TMP files just contain indecipherable gibberish only usable by the application that created them. Temporary files are often be deleted by the program that generated them, however sometimes, due to a software crash or poor software design the file extension TMP files aren’t removed and, potentially can take up a substantial amount of room on your hard disk.
If you see files with file extension TMP on your hard disk, they are usually safe to remove if they are older than a few weeks and you have no software currently running on your system. Given that there are no specific guidelines on the use or structure of TMP files, it is impossible to tell whether they contain information vital to the running of an application or not, and should therefore not be deleted unless it is absolutely certain that they are no longer required.
You may want to back up the TMP files first, wait a few days, then when you are sure there are no conflicts with your system, you may delete them.