瑜伽師地論略纂 2.78

2.78

「無色界有處所」者，業果異故，即於入定死處而施設故。　「無處所」者，謂無色身。或現定色故，名有處所；無異熟身故，名無處所。

Regarding "the formless realm has locations": because the fruits of karma differ, they are posited based on the places where one entered absorption and died. Regarding "having no locations": this means having no physical form. Alternatively, because form born of absorption is manifested, it is called "having locations"; because there is no retributive physical body (vipāka-kāya), it is called "having no locations".