Dragging and dropping a file from Bridge or Lightroom on top of an open document in Photoshop will (by default) place the file as an embedded Smart Object.
• Resize Image During Place – this will automatically scale down any file that is placed into a document smaller than it. But don’t worry, because Photoshop converts the file being placed into a Smart Object before it scales it down, all of the original data is there if you need to transform it larger.
• Always Create Smart Objects when Placing – this converts the file to be placed into a Smart Object. If you have reason to place an image as a regular, pixel based layer, uncheck this option.