Ontology imports allow you to easily reuse the contents of existing ontologies without having to add all their triples to your ontology yourself. For instance, you may want to build on a top-level ontology such as
BFO as a sound basis for your own ontology or use the information captured in a domain ontology such as
MAnufacturing's Semantics ONtology.
Consequently, benefits of imports include a reduction in workload, a reduction in file size, and they may also help with dependency management/ versioning, see
W3C