Although playgrounds can be very powerful for interacting with code, there are some limitations that are worth being aware of. There is no debugging support in the playground. It is not possible to add a breakpoint and use the debugger and find out what the values are. Given that the UI allows tracking values—and that it's very easy to add new lines with just the value to be tracked—this is not much of a hardship. Other limitations of playgrounds include:
Only the simulator can be used for the execution of iOS-based playgrounds. This prevents the use of hardware-specific features that might only be present on a device.
The performance of playground scripts is mainly driven based on how many lines are executed and how much output is saved by the debugger. It should not be used to test the performance of performance-sensitive code.
Although the playground is well suited to present user interface components, it cannot be used for user input.