Effects loop and tuner functions on my amp

I have a Markbass F1 head that has an effects loop and a tuner out.

What would be the advantage to running my effects in parallel vs. series. I guess it can be modified by a service pro to series? At least thats what the manual says. I think it might have something to do with if an effect goes out the main signal is still there.

Using the tuner function, can i just put a tuner pedal in there and tune with that? Would it mute the signal when im tuning or is it more for rack tuners and being able to tune when your playing?

the amp is at my friends house so im not able to try it out right now