I like to use a cream of mushroom sauce for pasta dishes and a vegetable soup for pies as it's cheaper and quicker than making your own sauce. I use a packet soup because you can control how thick you want the sauce and then you can save the rest for later. An added bonus, most are in cans so they last longer and you can use half as a sauce and then half for a bowl of soup.
I've done this before, and I find that it can work well. I also use spicy soups as a sauce in stir fries. I can adjust the spiciness by adding a little cream if it's too spicy or adding a little more spice if I want it hotter but it's much quicker than making it from scratch. As I have food allergies though I find even buying soups I can eat can be really difficult, so more often than not I end up making the sauce anyway.
