The extension recently had an update that now allows the recorder to highlight important areas on the screen with a mouse pointer or pen feature. Here is a quick video that will show you the latest updates.
If your Screencastify hasn't made the update you can right click on the Chrome extension, remove from Chrome and then re-add in from the web store.
The new tab tools (mouse pointer and pen) work on the majority of websites. If you start recording and the tools don't appear you know you have found one of those websites where the tools are not enabled.