Smart object
A smart object is a layer that preserves its source data, so you can scale, rotate and edit it without quality loss. Filters you apply become smart filters: always re-adjustable. It is the non-destructive way to work with placed images or RAW files.
Convert a layer into a smart object via right-click, Convert to Smart Object. It is especially handy when you want to resize a photo up and down repeatedly, because the original resolution is kept. Place a RAW file as a smart object and you can re-apply the Camera Raw filter to it again and again. Tip: double-click the smart object to open and edit its contents separately.
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The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.