It’s great to learn how things work.
Originally, this idea applied to cars. If you were going to own and maintain a car, you should look under the hood and learn what all the parts are. Learn what each component’s function is. This way, when the car breaks, you will know what’s wrong with it, and possibly be able to fix it. And if not, you’ll be better informed when visiting a mechanic.
The same idea applied to personal computers. Any time a new PC was purchased, I would encourage people to open it up and look inside. What kind of memory, CPU, motherboard, and video card did it have? If one had to upgrade the memory or install a new card, where would it go? Later when it was time to repair or upgrade the computer, you would be prepared.
Today, this concept works great on open-source software. Some people take the functions for granted and just want to use the components. It is a much better practice to actually open up the source code and understand how it was all put together. You can learn more about the features this way, especially if the documentation is weak. Open-source software can also be a great example of well-written code, because of the hundreds of code reviewers. You may learn some new techniques by studying the source code.
And if you don’t have access to your new tool’s source code? Read the manuals and know your APIs. Even if the software isn’t open-source, you should still learn everything you can about it. There can be very useful features hidden in the far corners of the documentation. Seek out the gems.