Blender 4.3

Like others have mentioned, Blender has become quite the successful open-source story. They used to be riddled with bugs and UX issues, much like FreeCAD was. Yesterday FreeCAD released v1 of their software, and they seem to be on the same redemption path as Blender. It's too bad their v1 release didn't gain much traction on here, as more people ought to give FreeCAD another whirl. The improvements there are massive. And it's the only proper parametric CAD software available on Linux.

To what extent can Blender replace FreeCAD for mechanical engineering purposes?

I would say avoid it. blender is an excellent MESH modeler but that puts it fundamentally at odds with being a good parametric modeler. a parametric modeler's base primitives are based in deformations on solid objects. mesh modelers are just vertices connected by line segments where 3 form a face. servicable if you're just doing simple objects for a 3d printer but disastrous if you need precision.

I don't understand why precision would be an issue? Is it not possible to fix the position of vertices to sub-micron precision?

I know that Blender is used more in the movie industry. But what if I wanted to make, say, an animation of some cartoon character that gets shredded in a gearbox? What program would I use?

A curve in a parametric CAD program will have an internal representation which is perfectly smooth. As rather than being than a set of straight lines (edges) connected by vertices it is instead a mathematical description of a curve which has infinite resolution.

For your animation example Blender would be the appropriate tool to use as you are doing stuff that requires flexibility of form rather than precision.

Aha, so it is a bit like bitmap versus vector graphics in 2d painting programs.