Hello Maxdamage,
the routing selects between parallel or serial processing for FX2/FX3. I recommend to set 'mix' to the maximum
value to hear the difference between the routings.
A parallel routing can be usefull if you want to combine 'reverb' + 'delay' or for special effects. The output of both effects in summed.
A serial routing is usefull for the most cases. It processes all effects in a chain. The output of the effect before is routed to the input of the next one.
Best Regards,
Markus Feil