You can delete the expression. It’s switched off anyway, once it’s been converted.
To set your work area, move the play back head to a point… press B…for Beginning then move it to a later point… press N for eNd.
Now you’ve set your work area. You’ll only get key points between those in and outs when you convert expressions to key frames.
Baking is used as a general term for changing anything that’s dynamically generated into something immutable. You’ll also hear about baking textures / particles / dynamics etc. if you use 3D. It stops the program having to do the calculations and converts those calculated values into keyframes that are remembered by the program… a list of values.
If you make an Expression Slider and set its value to 85.
Then on the rotation property, you write the simple expression…
r = effect(“Slider Control”)(1).value;
Then the layer will jump to a rotation of 85 degrees. If you change the slider, then the rotation will also change… but if you first bake the expression into keyframes, then change the slider… nothing happens. The frames have all been baked at 85.
Baked is baked. After Effects retains the expression, but disables it, in case at any point you want to go back to the dynamically generated value.