The player can check which TM a Used TM used to be by checking the item's description. A Used TM for Recycle cannot be restored.
Inside dungeons, a Used TM can be thrown at enemies to inflict 1 point of damage if the enemy already is holding an item. In addition, a Used TM will have a different appearance than an ordinary TM when seen on the floor of a dungeon.
The player is unable to store a Used TM. This is likely so that the game will not forget which TM it used to be.
This item is not present in Gates to Infinity or Super Mystery Dungeon. In Gates to Infinity, this is because TMs can be used infinitely. In Super Mystery Dungeon, though some TMs are single-use, those TMs disappear after being used (with Recycle 'restoring' Plain Seeds instead). The item is also not present in Rescue Team DX, though in that game TMs can no longer be restored with Recycle, and are destroyed instead of becoming used.