Don't jump to conclusions, Derren!
It isn't a feat, it is a replacement class ability that a paladin could have instead of his mount.
You don't get that many smite evils a day, and it means that if you do a charging smite evil you can get +(3*level) damage instead of +level damage.
If you compare that with a mounted paladin using spirited charge (and especially with a lance) doing smite evil, you'll see that this has considerably lower total damage potential, balanced by being available somewhat more often.
FWIW I don't see an awful lot of paladin minmaxing feats anyway - unless you are thinking of "divine" feats which they use their turn attempts for?
Cheers