To contain gutta-percha within the canal, instrumentation should result in:
The instrumentation and obturation should not extend beyond the apical foramen.
Whereas the guideline of 1 mm from the radiographic apex remains rational when using radiographs, the point of apical termination of the preparation and obturation remains empirical.
The need to compact the gutta-percha and sealer against the apical dentin matrix (constriction of the canal) is necessary to prevent extrusion of materials into the periapical tissues.

Textbook of Endodontics 3rd Ed P:
Cleaning beyond the anatomic apex
Cleaning beyond the radiographic apex
A cylindrical canal shape
The narrowest cross-sectional diameter at the terminus