Is Swapping Oil Each Oil Change Bad

[Gohn 68]

The automotive chainstores here quite often sell oil cheap to get people to go into their shops - 'loss leaders'

So I buy oil ahead of when I need to do a change, at good prices

Only problem is, the shops keep changing which oil they discount, so I've got three types on the shelf

Then, when I do my regular oil/filter change at about 8000km, I'll change from one brand to another

And each time, even though I warm it up first, then allow the sump to fully drain, its still got a bit left in the bottom due to the shape of the sump

Will that remainder be enough to spoil the new oil ?

I've heard rumours that its bad to mix oils etc but I just wonder what the consensus is

mostly I use 15W-40 or 10W-40 synthetic

[Leslie green 109]

I don't think it will make any difference there will always be oil left in the oil galleries and oil pump that doesn't get changed