Nope, that's it.
Longer barrel = more velocity. That means less elevation to reach long range. Also, the faster the round is (with all other factors being equal), the better it will buck wind.
Shorter barrels are lighter weight (if all else is equal) and more portable.
Everything is a trade-off. 20", give or take, is all you really need with a .308, or most other short action calibers.