More than one person has told me that we should rename SolidWorks Flow Simulation to SolidWorks Flow and Thermal Simulation, because (a) it does a lot more than just flow calculations and (b) it is the best design tool to use for thermal simulation especially when convection is involved. I'll have to agree with them solely for the fact that it would make my job a little bit easier.
Temperature plays such a large role in fluid dynamics that you cannot uncouple it from the solution; a great example in point is any material property, such as density and viscosity, that are very temperature dependent. The change in density due to heating and cooling is what drives the flow in natural convection. Thus you have air (or the environmental fluid) moving and convection is going on everywhere all the time, with the exception of when a body is sitting in a vacuum where there is no environmental fluid.
The convective heat transfer rate also varies widely over a given surface because it depends on many factors, such as: geometry, orientation to gravity, temperature of solid and fluid, material of solid and the type of surrounding fluid, and velocity of the fluid. If one trys to get a uniform averaged value over a surface, even with the best tables or hand calcs, it'll be a ballpark figure at best and assuming it to be uniform can neglect a lot of the physics. SW Flow Simulation does the calculating and consideration of all these factors because it knows the geometry and the flow equation is applied to the 3 conservation methods: mass, momentum, and energy (energy conservation being the thermal calculation part). It takes longer to manually calculate the heat transfer coefficient for every surface in contact with the surrounding fluid, so we're all too lazy (and in this case rightfully so) to take the time to do this and hence just collectively apply a single value for many surfaces.
Consider this picture of a custom heat sink showing contours of convective heat transfer coefficient; could you get a good average heat transfer coefficient from this model? I'll say no.
So in summary, SW Flow Simulation is the best tool for Thermal analysis because the correct handling of convection, both forced and free, is crucial in getting accurate results that best matches the physics of a real-world design.