When should I copy top-player talents?

Copying a top build is fine, but make sure you understand what the build is solving. Raid boss damage, dungeon route, arena matchup, and personal gear can all change talent choices.

Dungeon talents especially depend on route. A stop, dispel, or defensive can be worth more than a tiny throughput node.

Use copied talents as a baseline, then write down what you changed and why. That is how you stop cargo-culting builds.