Unity3D supports .psd and .blend and offers fast workflows with this option. Just drag and drop a .psd or .blend file into the asset library. Now you can open the file with your .psd editing-programm (Photoshop, GIMP or Krita) and make some changes. Whenever you save your file, Unity will automatically recognize the modification and update the file in your Unity3D project. The same goes for .blend files which can be modified with Blender.
This awesome feature provides a way to see the results of your changes directly in Unity3D. Think about making changes to a model or texture.
This feature does not have any impact to the final compiled game.
Every .psd will be converted to what you set in inspector. For example RGB(A). For the Blender file, Unity doesn’t really import the .blend file, it just makes Blender open in the background and export .fbx which is then used for your final compiled game.
But there is tiny a downside you have to be aware of. The .psd and .blend files store application specific informations. This leads to larger files sizes then .png or .fbx. But this only matters for your project size and not your released and compiled game size.