When to Use Greedy

Use greedy when:

$1.$ The problem has optimal substructure and greedy choice property

$2.$ You can prove that a local optimum leads to a global optimum

$3.$ Making a choice doesn't require knowing future inputs

$4.$ You can swap a non-greedy choice with a greedy one without worsening the solution

If you can't sketch a proof, consider DP instead. Greedy that works by accident fails on edge cases.