In general it's a widely accepted practice that you only run one malware removal tool at a time. Most Antivirus companies, and malware removal forums will suggest this.
I however don't always adhere to this, but I am selective as to what tools I will run doubled up at once.
Sometimes I'll run Malwarebytes, and SAS, or Malwarebytes and HitmanPro. Don't ever run Combofix with other running apps, it clearly tells you not to do so, and although I have never done this, to see that it can cause damage to a system, I trust that they know what they're talking about.