I think that Sainsburys and the other UK supermarkets are a complete rip off, so no, generally not good value for money.

Found quality and stock control at Sainsburys to be variable at best (as has been covered by another thread) and as a result, conducted an experiment. We bought our meat, fish and vegetables from butcher, fishmonger and greengrocer. All the rest, still sourced from a supermarket. Now the trick here is to only buy what you need.

Have found, and this has now been our normal behaviour for many years now, that this approach is cost neutral. The added advantages are that the food quality is far higher than from a supermarket and very little is wasted. The downside is that the shop takes longer and requires planning.

So, in conclusion, one pays for convenience at a supermarket, and little else. We also, when pressed for time, will do this. I guess on those occasions, it is value for money, as we have bought the time to pursue another activity.