What to watch out for when running two instances of Hashcat at once?

[slyexe]

What is the significance of this? Just do multiple cmds in a bat file. 

hashcat.exe -m xxx -w 3 -a 3 etc...
hashcat.exe -m xxx -w 3 -a 0 etc...
pause

If you do 2 instances, you're just going to be splitting the workload and straining your system. So why not just finish one attack and get full potential out of both of them.