IMPLICIT tagging is used in PKIX (and other protocols) whenever a context or application tag is needed to disambiguate due to either a) OPTIONAL members, b) members that were inserted as if the SEQUENCEs/SETs were extensible, or c) CHOICEs. The reason for IMPLICIT tagging instead of EXPLICIT is simply to optimize on space: if you use EXPLICIT you add a constructed tag-length in front of the value that already has a tag and length, but if you use IMPLICIT then you merely _replace_ the tag of the value, thus with IMPLICIT you save the bytes for one tag and one length.

Kerberos uses EXPLICIT tagging, and it uses context tags for every SEQUENCE member, so these extra tags and lengths add up, but yeah, dumpasn1 on a Kerberos PDU (if you have the plaintext of it) is more usable than on a PKIX value.