Try to give you the simplest answer.
Four ways to use well Caste system:
1. GS Strategy - use Caste system + Pacifism (if possible) + NE (if possible) to generate GS points. A GS can bulb +1600 beakers, which means you can use one to bulb Philosophy, Paper or 1/2 Education. It's the most efficient way to beeline Liberalism.
2. GM Strategy - use Caste system + Pacifism (if possible) + NE (if possible) to generate GM points. A GS can make 1100 gold in the Middle Age, 1700 gold in Renaissance et 1900+ in Industry Age. A powerful way to support a 100% Research, especially when you're at war.
3. GA Strategy - use Caste system + Pacifism (if possible) + NE (if possible) to generate GA points. A GA can bomb 4000 culture for a city. Best way to rush a culture victory.
4. Maximize your workshops' output - a workshop Cast system + Guide + Chemistry give you more output than a mine before railway, let alone +1 food given by SS. This is always the reason why I stick to Caste system till the end of the game.