Sometimes you can get a joint together no problem. But getting it apart is another matter.
With the joints for a heavy French workbench, disassembling a test-fit gives many beginning woodworkers a fit. Many times they end up slamming hammers or mallets on places that are easily bruised (including their hands).
The easiest way to knock out a leg that I’ve found is shown here. Prop up one end of the workbench top onto something that lifts the legs off the ground by 6” or so. Get a sledge. The one I’m using in the video is 2-1/2 lbs. A heavier sledge is faster, but it can make a bigger dent if you miss your mark.
Then get a scrap of wood that is smaller than the mortise. Use the scrap to knock the leg out of the mortise. The trick is to use multiple controlled taps. Big Thor-like expressions of your masculinity are not necessary.
As the leg starts to drop, put your foot under the leg to prevent it from getting dinged from its final fall.
The legs shown in the video were incredibly tight going in. Controlled taps with a small sledge made them easy to remove.
— Christopher Schwarz