To me...it makes sense to mix oils. I scored a load of Mobil1, PYB, Castrol GTX, Syntec synthetic, Edge, Valvoline White Bottle, Valvoline SM Red Jug MaxLife and Castrol 15w-40, Tection at Kmart clearance sales on Gallons.
I change the oil for Family, Friends, neighbors and the elderly and no oil goes to waste. The used oil and filters are disposed of properly, by bringing it back to the various Auto Shops for recycling.
For my use....Most vehicles that use oil,take more than a Gallon and some can't use heavy oils. So I'll blend the oils of different viscosity's with other....ALL IN THE SAME FAMILY....if possible to get the weight oil that I need.
Buying lots of oil, in quarts and jugs, off the clearance racks at Kmart, WM, Advance, AZ and O'Reilly has been helpful to add to some heavy grades....made by the same Family.
I have found a use for Castrol Synblend 20w-50, Castrol Edge 5w-50, Mobil 1 15w-50, Valvoline Durablend 10w-40 and 15w-40, Valvoline MaxLife 10w-40.....and so on....
I just add some of the same Brand and Type of oil in a lighter viscosity of 0w,5w-20 or 30 to get what I need.
Even Mobil 1 states, in it's frequently asked questions section....that all Mobil 1 oils are compatible with one another and can be blended or mixed with each other.
In fact I'm now running 2 different grades of Mobil 1 oils that I picked up at various Kmart store closings in Orlando, Fl. IMO...very good oil at a very good price.
In fact....I'm now about to pull the trigger on a couple of cases of Mag 1, HD Fleet Oil, 10w-30 on Amazon.
This oil should mix and blend very well with another product that I picked up at AAP, during the summer, on clearance for $1.95 a quart....Peak Full Synthetic 5w-20.
I say....mix and blend away, within the same Brand and Family, if possible.