Home is Procol's fourth album; it found them at something of a crossroads, having seen the resignations of Matthew Fisher and David Knights (bass player) following A Salty Dog, widely acknowledged as PH's masterpiece.  They took a page from the Doors' book, hiring Chris Copping to double on keyboards and bass (a la Ray Manzarek, who often added keyboard bass on stage and, on the first 2 LPs at least, in the studio - they did use actual bassists from Waiting for the Sun onward in the studio, such as Doug Lubahn); whenever a song could do without guitar, Robin Trower took up the bass and Copping focused on the keys.  The quarter formula seems to have worked out well for them.