A tree may need to be removed if it is overgrowing its space or if it poses a threat to human life, public safety, or property. A dead or diseased tree is a disaster waiting to happen. A falling branch could do a lot of damage.
Tree removal is usually best left to professional arborists, since much of the equipment is dangerous and may require training. If you choose to remove a tree yourself, follow all safety protocols, and make sure you know exactly how to operate the equipment so that neither you nor your property are injured.
Tree removal may require the use of a crane or logistical engineering. In this case, the professional arborist should be employed.
However you choose to remove your tree, observe all necessary precautions to keep you and your yard safe.