Yes, you can look at this blog for various examples. http://socpuppet.blogspot.com/2018/07/howto-use-fortios-api-to-add-delete.htmlhttp://socpuppet.blogspot.com/2019/09/howto-use-fortios-apiuser.html
The last link shows a system wide get for monitoring firewall policy. Using the API you can ascertain counts for all policyid with out specifically apply them. This is an advantage over the diag firewal iprope show cmd which requires a "specific policyid" # to be included.
YMMV but the API is more advance for monitoring.
With either approach they help in auditing and identifying bad policy, or policy not being used. Policyid with no hits comes down to;
policy written wrong (src/dst-addr|interface, incorrect service, typo,...... )
or the request/project for that policy-rule no longer exist
Again YMMV on how you use the counts and hits. If I'm doing a project and audit. I always monitor the hits and last used time values in order to flag policyid thare no longer needed or to flag them for later review.
If you have a policyid and it has been used in 3+ month you probably do not need it