Are certification courses like ISTQB necessary in testing career and if so, to what extent?
How will certification help in a testing career and up to what extent will it help?
Is certification courses like ISTQB necessary in testing career
It's clearly not necessary, as the many non-certified testers can attest. I have been in this business a long time, and have never felt the need to become certified. And I have hired a lot of people - never once requiring or caring if they were certified.
In my experience, for the certified, it's not actually the certification that is useful, but the learning that is actually useful.
In my opinion, you can gain all the knowledge you need on your own, or you can go spend money on certification courses and gain some knowledge (which may or may not actually be useful/needed).
A while back, I performed a quick experiment to see if certifications were actually useful in getting hired. My conclusion - "So will having a CSTE or CSQA help you get hired? Perhaps. But it probably won't matter."
You can try a similar experiment yourself: Software QA Certifications - An Aid To Gaining Employment?