Postgis 4326 geometry vs geography

There is a big difference. Geography is much more precise, though much more resource intensive. Geometry will eg produce distances in the SRID units (degrees) that have little meaning to you. Geometry treats lines as lines in the projected surface while in reality directs from point A to point B are arcs of great circles (meaning geometry will return incorrect results for intersections etc).

In short, geometry uses planar geometry vs geodetic calculations on an ellipsoid.