Learning about certificates in appsCA.pem

[dc17]

HI, 

I am trying to learn more about the certificates found within the document /etc/auth/appsCA.pem .

I'm referring to Splunk's default certificates, Global Sign Root CA, Global Sign ECC, DigiCert Global Root, ISRG Root, IdenTrust Commercial Root.

Are they safe? After changing the certificate configuration with my self-signed certificates and merging the CA Splunk certificates to make Splunkbase work properly ( This case here ), I wondered if they are all necessary for Splunk to work successfully or only some of them.
Is there a documentation page or can someone explain the use of each of the certificates?

Thanks in advance,