Endocervical sampling is recommended during colposcopy in the following situation
Recommendations for Endocervical sampling:

Colposcopy in inadequate, or colposcopy is adequate but no lesion is identified. Endocervical sampling is acceptable in other cases at provider discretion.
Initial evaluation of ASC - H, HSIL, AGC, or AIS cytology test results.
Surveillance 4 to 6 months after excisional therapy if specimen margins are positive of HSIL.
Surveillance after conization for AIS has been performed in women wishing fertility preservation. Negative endocervical curettage results add reassurance to this management.
Initial evaluation of LSIL in pregnant female
Surveillance 4 to 6 months after excisional therapy if specimen margins are positive for HSIL
Along with co-testing in post-menopausal LSIL
Reassure LSIL patients in age group of 25 to 30 years.