The fundamental difference is that the former is adjusted for this layer, and after adjustment, the layer changes and is not repaired. Also, if you want to continue with the adjustment later, you can only readjust the result as a starting point for the last adjustment. The latter is a new layer that adjusts the layer, and the layer itself does not change, and you can later make changes to the last adjusted data directly on the adjustment layer, throwing or closing the adjustment layer directly if you want to undo or not show the effect. (Other adjustments, such as curves, etc. and similar to this)
Also, when you resize a selection within a layer, the selection is displayed when you use the Adjust command, and the selection is invisible when you adjust the adjustment layer, which means that the adjustment can see the overall effect while adjusting.
However, note that when you use the adjustment layer, if you want to convert the image mode (such as RGB-CMYK) the computer will remind you to throw away the adjustment layer or merge all the layers. If you want to apply an adjustment layer effect without merging all layers, you can merge the adjustment layer with the adjusted layer before converting mode, and then choose not to merge when you convert.Classification: