I would not want to broadbrush that mold is not that dangerous. Every property management company I've dealt with treats it seriously. While many people don't have negative reactions to most kinds of household molds, mold does cause some people with respiratory sensitivity or other ailments to have adverse reactions. As a landlord, unless you know your tenant's medical situation, it is always prudent to take action promptly.
About 10 years ago, we had a property in Chino where the tenant sued the ownership due to health issues resulting from mold in their unit. Turns out there was mold forming on the wall behind their bed due to the close proximity of the headboard to the wall. During winter months, the weather can get down into the 30's and this was causing the inside of the wall to sweat as the interior of the unit was kept at a much higher temperature. When the onsite manager learnt of the problem, she immediately had the onsite maintenance crew help move the tenant into another vacant unit. With larger properties, all maintenance requests are documented and there was no evidence that the tenant had brought this issue up in the past. Due to the manager's proactive efforts, the tenant did not win any monetary award.