It's summoning without having to train summoning! Of course it's good!
For convenience, use = to map your arrows to b. Make sure nothing is mapped to a. You can then uses ' to swap back and forth from unarmed to arrow weilding in one key press.
Things S2S is good for:
- Guaranteed summoning spell, in your first book, that trains with one of your key skills
- Additional sources of damage in a fight.
- Poison.
- Crowd control (many v many is better than going up against a crowd alone).
- Overwhelming Snake Spam (not recommended or doable early on, but occasionally worth it later).
- Distracts enemies- they take some of the hits.
- Retreat aids- keeps the enemy busy, or blocks hallways.
You can also use spears / javelins / giant clubs (well, not as a naga) / magic staffs. Bigger things have better odds of better snakes, but since they're equips they have a chance of being cursed (unlike arrows). And cursed weapons will often make hostile snakes.
If there's anything you don't want to accidentally snake-ify (a staff for example) inscribe it with !D.