When you opt for a policy physically, the insurance guys do your urine test, stool test, heart rate etc., and then issue a certificate saying that he/she has these problems which won't be covered if claimed for.
As for internet policy, the details you key in are the details company receives, which means if you have a bed wetting problem (am not saying you, just a wild example), and if you put a claim tomorrow saying you have to undergo a surgery for the ailment, getting the claim will give you various ailments like nausea, loose motions, piles etc., as there was no proof to show that you were 100% fit when you took the policy online.
Again, don't take my word, take a dip and buy a policy online and then file a claim.
As always, I recommend to opt for LIC or GIC policies as they are very transparent and reliable, private players are here to screw up the common man.
Again, don't take my word, experience yourself