Not sure what you mean, here...
If the card restores a percentage of a player's TP over 20 seconds, it'll be useful in
every single circumstance that the cost reduction is useful, plus THESE (where reduction would be worthless):
-The player is missing TP but stunned or otherwise unable to use their abilities (like no target to hit at that moment), but they will still benefit from the restored TP after the buff runs out
-The player has run out of TP and will benefit from having their TP restored since they have none to spend
-The player doesn't notice that they have the buff on them for whatever reason but they will still benefit from the extra TP when they next look at their bar and see they have more leeway
Can you name an example where the reduction is superior to the restoration?