rewrite_rules entry in options table

In the last couple of days, after 18 or so months of the site being in place, the entry ‘rewrite-rules’ has been created in my options table. It is enormous. Scanning to the end, it is also truncated. It also, oddly, was not created with the next ‘auto’ number in options but given a much higher id key.

My questions are really:
Why did this suddenly get created?
What were the circumstances that caused it to get created?
Is it actually required?
Does it matter that it appears to be truncated mid-word?

I see that others have raised questions before with this option row that suggest it can lead to problems? None seem to be answered. Shoud I be worried?

Thanks for any help and advice…