Visuddhimagga III-59

Evaṃ bahūpakārattā sabbattha atthayitabbaṃ icchitabbanti ca adhippetassa yogānuyogakammassa ṭhānañcāti sabbatthakakammaṭṭhānanti vuccati.

因为（慈与死念及不净想）有这样多的利益，所以当于一切处希求，其目的便是勤修瑜伽的业处，故名为「一切处业处」。

Ñ(III,59): So these are called generally useful and they are called meditation subjects since they are needed generally and desirable owing to their great helpfulness and since they are subjects for the meditation work intended.