This operation divides one or more target bodies using a datum plane or sheet body. Separate Body is the same as Split Body except that the "split" is fully associative to the cutting geometry. Separate Body can be accessed from the Modeling application at Insert->Trim->Separate Body....
You must select at least one target body, even when there is only one possible target displayed.
You can select a datum plane or sheet body to separate the target bodies.
Non-Manifold Solid |
To use the Separate Body option, follow these steps:
Separate Body is really a convenience function that automates several modeling operations. To demostrate the operation and show the end result, lets create a block and separate it using a sheet body. Below is the model that will separated. The block is in green and sheet body is in yellow.

As shown in the model navigator, the sheet body was created using a sketch attached to the block face and extruded direction and distance.

After running Separate Body and picking the block as the target and selecting the sheet body as the cutting plane, the following model is the result. Notice that the block is now two solids( the original is green and the new one is orange). The separation of the two solids is along the sheet body.

Looking at the model navigator reveals three features were created.

The result is now if you change the sketch curve, the two solids will also change.