The Solver Model used for FE Chasedown is generated as part of the combined analysis and design process if the model contains flat slabs, or two way spanning slabs on beams - the results from this analysis being required for the design of these slabs.
By default the same results are also used to generate a third set of design forces for the cast-in-place beams, columns and walls. (Whether the results are used for this purpose is controlled by a setting under Design > Settings > Concrete > Cast-in-place > Beam, Column, Wall > General Parameters).
A significant consideration when opting to design for the FE chasedown results is that the slabs will tend to carry a significant proportion of the load direct to the columns.
Consequently, for beam design in particular, it is unlikely that an FE chasedown could result in a more critical set of design forces than would be already catered for by the Grillage chasedown.
Note: If duplicate levels have been specified in the Construction Levels dialog separate sub models are created and analyzed for the source and every duplicate level. This ensures that the increasing load carried by the vertical members in the lower sub models is catered for. In turn this can cause small differences in the analysis results (and consequently the design) for these sub models.