It's great for getting into Salisbury without having to find a parking space. Regular buses whisk you into town and there's no restriction on time, within shopping hours that is.
Good idea to use a P&R in Salisbury. When I used it the fare was still free but charging has recommenced and is good value. Watch out on the way back as the stop is after the P&R building.
Useful P&R and good value if you are travelling as a couple or a group. Takes you right to the centre of Salusbury with little fuss.