It’s not necessary in most cases, but it has advantages. Namely, it’s easier to work with and melts at lower temperatures (less risk of damaging components and burning yourself). Also, while lead has its risks, they’re easy enough to mitigate.

Lots of conjecture and misunderstanding in the other comments. Thanks for posting actual sources.

Be ready to replace the disk when the warranty ends.

What’s the point of replacing them? The warranty doesn’t keep them from dying, it just means you get a free replacement. The amount of life left on the drives after the warranty expires depends heavily on how they’re used, and most self hosters are pretty gentle on their drives. I could see replacing the drives that are heavily used, but replacing all drives just because their warranty expired seems like a waste of money and effort.