Why blend different oils?

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Why do some blend different oils?

Example: I have seen on this forum, some people will blend 3 quarts of 5w30 and then 2 quarts of 10w30. Or, 4 quarts of 0W-20 and then a quart of 15W-50.

I am not talking about just using up the last few bottles in a stash, I am talking about intentionally blending particular weights.

What I wanna know is, what benefits would it have? Let's say, for example, that I have a 5 quart engine capacity, and I blend 3 quarts of Mobil 1 0W-20 with 2 Quarts of 10W-40. Why would I want to do that? Would that mix have any characteristics that are better than 5 quarts of Mobil 1 5w30?

Thank you very much, I just don't understand.

 

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I can only explain it by recounting the way I mix oils, for viscosity. That's to say, not every instance is one where I want to blend oil, but have a leftover oil that is close to the oil used inthe fill, say a Mobil 1 5w30 in with some 0w-30....just because it's what I have stocked. Now, you can thicken or thin an oil a bit, that's fine, but I only do it with a known similar oil, say Havoline 5w30 with 5w-20. I've often done that to fine a visc that is best suited, even before coming to BitOG, in 2002.

 

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Say you want to use...DuraBlend, but the 10w-40 is kinda thick, and it's winter, so maybe you mix it 50/50 with 5w30. I have a lot of Delo 30 here, I use it as a bit of a filler with Havoline 5w30 in winter, but mix it with just a splash of 40 weight for summer in my Euro cars.