Concentric guardrings are common in ESD related circuitry
(pad cells etc.). One useful function is that the built-in
depletion region is a "getter" for loose minority carriers in
the substrate. The ring can also kill lateral BJTs' base
ohmically and deterministically if it is closed / pervasive,
fight field oxide inversion / charging and so on.
Cost sensitive folks might find it uneconomical but "must
not fail" folks see it as another dose of tonic.
Thanks for your response. Is there any material regarding this? That ill b better to know more about guard ring. kindly share it if you have any documents.