Interesting, I've never thought of the spark arrestor as a safety feature. I guess theoretically it prevents starting a fire in dry conditions, which is a good thing.

My chainsaws came with two safety features: the kick guard (or handguard) and a tip protector. For those who don't know, the kick guard sits above your forward hand and stops the chain immediately if you push it forward. If the tip of your chain catches a log juuust right, and you aren't holding the saw firmly with both hands, it can "kick" the chain up towards your face. If that happens, the kick guard will hit your hand and stop the chain. You take a deep breath, pull the kick guard back to release the chain, and keep working. I don't know why anyone would remove it, or if it's even possible for my saws to run without it.

The tip protector is intended to prevent kickback at all, by keeping the tip of the bar from contacting anything in the first place. That's fine if you're cutting stuff a few inches across, but it makes cutting large stuff impossible and even small stuff inconvenient. Kickback doesn't happen often, very rarely if you're careful, and the kick guard handles it, so I've never seen anyone cut with a tip protector. But if you're new to using a chainsaw, it's probably not a bad idea to keep it on.