One of the great things that came about in the development of T&T combat - way back in the late 70s/early 80s in an old issue of Sorcerer's Apprentice - is Spite Damage. It adds a great element of unpredictability to combat (that can often be pretty predictable after a foe's toughness is established, especially after it is wounded). Spite damage can really take its toll on a party however, greatly so at lower levels when PCs are wimpier and without magical protections against such things. For the decade or so now that I have been using Spite, it has really changed the dynamics of combat compared to what it used to be like in my early days of T&T.
In my games, when you roll a 6, you have several options:
1. use it for Spite
2. 'explode it' (i.e., count the 6 toward HPT and reroll)
3. use it for Anti-Spite (i.e., use it defensively to eliminate a point of the foe's Spite damage)
4. 'burn it' (This is one of my favorite options because it causes an interesting dynamic in the party. When you 'burn it', it doesn't count toward Spite, Anti-Spite or explode, but instead grants that player 50AP. This can be quite a temptation to quickly accumulate AP, but is often perceived by other players as selfish. On at least one occasion multiple 6s have been cashed in for a big AP payout, only to have that character die of Spite at the end of the combat round - Spite which could have been easily avoided by using the 6s toward the party's Anti-Spite total.)
The idea of burning the 6 has been batted around on the internet in various T&T related sites for at least a decade. It was eventually pinned down in a semi-official format, and thus may be most familiar to readers, as an option in the bootleg 6th edition of T&T.
Anyway, in my T&T I like KISS, but I also like choices for the players to make. This keeps it fresh and requires strategy on their part. These options allow for a KISSable way to offer strategic options. This, along with lots of Saving Rolls in combat to try various stunts, makes combat an exciting part of the game.