1. In Tool Age:
- Kill Watch Towers (amazing how fast just 3 of them knock down one Tower).
- Kill Bowmen (a boon against the deadly Bowmen rush! Without Slingers, it's goodbye Villagers...)
2. Bronze Age
With a little upgrade (that you need later for Siegecraft, anyway), they really shine again at killing Sentry Towers - just use 5 instead of 3 per Tower.
Again with the upgrade, they can help Roman Swordsman to fight CA, and are useable at helping against CA, but not that much, because CA fire from afar.
3. Iron Age
- Upgraded Slingers STILL take out Guard Towers - maybe 7 or 8 per Tower, for good measure.
Slingers are great wall busters!... Why desperate in front of a wall-in?... You CAN now penetrate it in Tool Age with the aid of Slingers, something you could never have done before!... their best abilities involve tearing down walls, killing bowmen and killing Towers. Highlight:
4. Slinger Competence for
In summary:
Breaking into a Tool Age wall-in is no little thing, rest assured.
One more thing that Your Old Friend here learned by losing...