It has its place; the key thing to remember about it is it's not sustainable.
Security by, say, mathematically-hard problems stays secure even when the problem's design is understood. Security by obscurity breaks any time the secret gets out.
(There is an overlap point where a math problem is too simple to solve and, meanwhile, an obscure secret is "The sixteen digit number the President memorized to launch the nukes" where the security-by-obscurity can even beat out mathematically-secure, but the middle points of those two sets are separate and the reliability heavily tilted in favor of the mathematical cryptography).
Security by, say, mathematically-hard problems stays secure even when the problem's design is understood. Security by obscurity breaks any time the secret gets out.
(There is an overlap point where a math problem is too simple to solve and, meanwhile, an obscure secret is "The sixteen digit number the President memorized to launch the nukes" where the security-by-obscurity can even beat out mathematically-secure, but the middle points of those two sets are separate and the reliability heavily tilted in favor of the mathematical cryptography).