When/If...
Tree is dead and posing potential to fall / windthrow,
Tree is suffer from severe disease and pest infection,
Tree is posing a threat to stakeholders and public,
Tree is at high angle above target e.g. building, pathway, traffic road,
Short of manpower or seeking alternative contractor,
etc...
See how tree removal by international standard method (from climbingarborist.com)
See how tree removal by rigging at high angle (from arborpod.com)