First is for creating a bolt pre-load when you actually want to analyze the whole bolt and not use an idealized beam element representation that is used in the bolt connector. There is a great video in the SolidWorks KB S-011370 about pins that also applies to bolts and why you might actually want to model the bolt in 3D.
The second use case is for a large press fit that might fail. If you have non-linear analysis you can shrink the female part at time =0 and then gently expand by coming to room temperature during the final time step. The value here is that a typical shrink fit contact is solved in one intital time step even in a non linear solution. By using no penetration contacts and thermal shrink and then expansion you can often solve a large shrink fit problem that might not have converged before.
Stay tuned to this blog post for a step by step process on how to estimate temperatures and implement bolt pre-load and shrink fits using thermal boundary conditions and no penetration contacts.