Why is it important to buy the policy with pre-existing health conditions coverage?

Insurance with Pre-existing health conditions coverage covers:

Injuries or illnesses that are new, as well as health complications related to problems the person has had in the past, if these are stable during the stability period determined by an insurance policy.

Insurance without Pre-existing health conditions coverage covers:

Injuries or illnesses that are new and unrelated to health problems the person has had before.