Photographing through windows is a popular motive in street photography. That physical barrier in a way separates the photographer from the subject and they appear as two different worlds. The barrier may also give additional comfort to a photographer who is anxious about taking photo of someone. It may be a good practice for someone just starting out. :)
For me, it's one of the ways to introduce more depth and dimension into the photograph. Reflection is often the key to making these kind of shots work. If the light is not good or the reflection is boring, the result will be a failure. Also, shots through windows may get messy with all the dimensions going on so it's important to separate the main subject while keeping the overall context of the scene.
Anyway, here are some of my examples, hope you enjoy. :)
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