Can I mix ABS and PLA when recycling filament? I'm thinking of recycling some filament from a couple of recently failed prints. I can reuse them in the future for basic prototypes, so I'm not concerned with whatever weird mixture of colors come out (they are of a few different colors).

The thing is, I have both PLA and ABS, in small quantities. I originally intended to simply use each one separately, but it occurred to me that they could be mixed.

If I recycle PLA and ABS together into one strand of filament, will there be any negative side effects (e.g. reduced strength)?
This is not a good idea. Both filaments have different melting points, that of ABS being much higher than that of PLA. To melt the ABS you have to heat the plastic to the point where the PLA starts to degrade.