You can create mesh objects from vector objects, with the exception of compound paths and text objects. You cannot create mesh objects from linked images.
To improve performance and redraw speed, keep the size of mesh objects to a minimum. Complex mesh objects can greatly reduce performance. Therefore, it is better to create a few small, simple mesh objects than to create a single, complex mesh object. When converting complex objects, use the Create Mesh command for the best results.
For more information on creating a gradient mesh object, see the Achieve photo realism with Gradient Mesh tutorial at www.adobe.com/go/learn_ai_tutorials_gradientmesh.