Hotspot hinting is a major way to cheat on usability tests. You should turn it off.
Note: hotspot hinting is the feature in prototyping tools that if you click somewhere in the prototype all the clickable elements will light up in blue.
If you leave hotspot hinting on, you will miss out on many many usability issues. Why?
Much of software usability revolves around whether users can find and recognize certain UI elements. E.g. Do they find the function that they need for their task? Do they notice the button at the bottom of the screen? Do they realize if something is a link and clickable?
If the user clicks somewhere and suddenly all the task-relevant buttons light up ...well you have just reduced your usability test into a simple "Can you see the blue light?" visual perception test. Now the user doesn't need to understand anything about the UI anymore. All they need to do is to follow the blue lights...
One of my colleagues liked to leave hotspot hinting on to spare users from the frustration of clicking around in prototypes to no avail. But there are other ways to manage this frustration: simply tell participants up-front that this is only a prototype and many buttons/links will not work, yet they should try to carry out the activities as usual.
It is indeed very important to see users clicking all over the prototype to no avail. You are not only learning that they can't find the desired function, but you are also learning why are they not finding it. Did they look for it in the wrong place? Did they see the function but assumed it was for something else? What were the places they were looking for it? That's where they expect it to be.