Not entirely unnecessary.

It's a big question as to why life started on Earth as soon as it did, pretty much as soon as it was even possible.

That could be because life is very easy to start if conditions are right. In which case it's quite likely to have started on early Mars too, and we should expect to find at least simple life all over the place.

The other possibility is that it didn't start on Earth, and was seeded from somewhere else.