Whether it's legally required depends on the destination; some countries and visa types, notably many short-stay visas, demand proof of insurance with minimum medical coverage, while others don't check at all. But required and needed are different questions. A single hospital stay abroad can cost more than years of premiums, and your home health system almost never follows you across borders, so for anything beyond a hop to a neighboring country with reciprocal care, insurance is money well spent.
The core coverage to insist on: emergency medical treatment and hospitalization with a genuinely high ceiling, medical evacuation and repatriation, which is the piece that gets ruinously expensive without cover, and personal liability. Trip cancellation, delay, and baggage cover are nice-to-haves that matter more for expensive prepaid trips.
Read the exclusions before buying: adventure activities, pre-existing conditions, and incidents involving alcohol are the classic gaps. And check your destination's embassy website, since where insurance is a visa condition, the policy usually has to meet specific stated minimums.