There are some people who can have reduced anxiety symptoms when they use cannabis. So for some people, cannabis may help with performance anxiety, also known as stage fright.
However, there are other problems that may arise when you resort to cannabis to help deal with your anxiety. When you use cannabis on a regular basis to reduce your anxiety symptoms, then you may find that the effect of the cannabis is reduced with each successive use of the cannabis. In other words, you may find that it takes more and more cannabis to get the same anxiolytic effect. This is known as tolerance, as it takes progressively increasing amounts of cannabis to get the same effect with repeated use.
Another problem that may arise is that your life becomes disrupted as you seek out the cannabis, as you may find that you will continue to use despite having serious consequences to your relationships, financial situation, and school/job performance. This is known as dependence, as you seek out the cannabis to the detriment to other important parts of your life.
So with repeated cannabis use to reduce anxiety, you may develop tolerance and dependence. With this, you risk developing an addiction to cannabis. This addiction becomes another added problem, in addition to the anxiety you are trying to deal with in the first place.
Another problem with chronic cannabis use is that it can result in cognitive problems, as it can affect your executive functioning, which is involved with planning, filtering, and initiating tasks. So your goal-oriented activities may become markedly reduced, and you may develop amotivational syndrome, where you have no ambition and have several other symptoms which resemble depression.
Paradoxically, some people who use cannabis may develop worsening anxiety.
Although cannabis may help some people to reduce anxiety over the short term, the long term use of cannabis can induce tolerance and dependence, leading to an addiction. Still, there are other people who might develop worsening anxiety when they use cannabis.
Here's the bottom line- cannabis is not helpful for anxiety, such as performance anxiety.