In addition to audience, it also depends on timing.
Not hard and fast rules but,
Concept generation - sketches
Concept refinement - shading
Concept finalization - renders
It also depends on how long you have had a client. Long-term ones tend to know the renderings are spendy and would rather see the lower cost sketches.
If the sketches are for the customer (end user, not client), it depends on the objective of the research. A rendering is real, a sketch is only an idea. The level of refinement can control expectations.