So far as software development goes, they are of limited value in the US job market. Most employers are interested in your college degree, not a certificate for passing tests.
There's also the issue of the certificate going stale rather quickly. For example, if you had earned a .NET certificate 5 years or so ago, a lot of what you learned to pass it would be outdated today.
Yet another issue is the cost of the certification and the lack of ROI. Having it probably won't increase your salary or land you a job (US market, may be different elsewhere). Oddly enough, companies are reluctant to pay for it because they are concerned you will leave if you get certified.
The positive side is that you will have to learn a lot of stuff to pass the tests, things you might not have been exposed to otherwise. You could do this on your own but having the motivation to pass a test helps some people learn more efficiently.
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