A quick way to estimate the value of any certification is to search for it in job requirements across websites where jobs are posted.
This can show you two things:
- The current demand for any given certification.
- A potential estimate on what jobs pay for people holding such a certification.
That said, something very specific to the certification you are asking about is if this is your first GIAC certification you'll also want to look into the jobs which require some form of GIAC certification but may not specifically list the one you have.
Finally, keep in mind that the certification itself does not directly relate to career growth unless you are leveraging it to do so by changing jobs or landing additional contracts, etc. There are lots of ways certifications can help but the value of any given certification will be unique to the person who earned it. Likewise, certifications may be of more value to contractors than to full-time employees because they will leverage it more often.
The benefits of most certifications are usually worthwhile because they can open more opportunities but at the same time they are indirect and hard to measure.
I also want to quickly point out that certifications are not the only way to do this. If you write cool software and post it on github or do any number of interesting projects you can leverage these in a similar manner and include them on your resume to put you ahead of your competition. In this respect certifications are mainly useful when working with recruiters that are looking to match minimum requirements.