As far as we know, there is no recommended time for saving insurance policies the way there is for tax returns and such. However, five years is a fairly reasonable time to keep something for reference. While an insured can certainly file a claim with a policy number and effective dates, you run into the prompt reporting provision. If an insured is careful enough to save policies, they should be careful enough to maintain the property. The only scenario I can think of where an insured wouldn't realize there was damage until several years later would be something like scarring or residual nerve damage from a dog bite to a neighbor that the neighbor experienced some time after the bite occurred.