When it comes to Structure extensions, such as Structure.Testy and Structure.Gantt, there are no known risks associated with the usage of Testy, but Structure.Gantt may require some attention.
Structure.Gantt uses actual Jira data for visualization of tasks on the timeline. Users can define, which custom fields are used for start and finish dates, what is used for the task estimation (Jira time tracking info, story points or some other fields) and what Jira link types are used for different types of dependencies.
This means that when a user changes any of these parameters in the Gantt chart (by resizing the bar, creating new or deleting existing dependencies, moving the bars to change the start and end dates), the user is modifying the real Jira data. The sandbox mode is coming in the future, but right now all the changes are done in real time.
The gantt chart visualizes the tasks on the timeline and with certain settings this may require some calculations. For example, you can use Structure formulas for calculating start/finish dates, estimates or progress. Visualizing tasks with dependencies may also require certain computational effort. Resource allocation is another part, which is calculated by Structure.Gantt.
While for smaller structures this should't be a problem, for larger projects, these calculations can add up, so it's recommended to try such configurations on a staging server first.
For more information please read the enterprise deployment notes.