Based on my readings, is it really better to not connect the grade beam to the ground floor slab to separate the structure from unnesseray movement of the ground?
It certainly depends on the nature of the soils but usually, when I've designed a perimeter grade beam foundation, say on drilled piers, the interior floor slab is always separated due to potential differential movements between the slab and the deeply supported grade beam.
In areas with expansive clays, this is even more critical with the grade beams built with small voids below them so when soil expands, the grade beams aren't forced upwards. The interior slabs in these situations are always kept separate as are interior walls separated from interior walls with slip joints.
You just need to be sensitive to the difference in future movements between grade beams (usually more substantially supported) and interior slabs (resting sometimes on questionably compacted subbases).
