For large spaces load calculation which is better, considering the space as one zone, or split it into multi zones? and why?

It mostly depends on the Zone. If the zone have multiple exposed walls than it is better to take it multiple zones to know which specific area needs more cooling. For example a big area with 4 exposed walls and one wall is totally glass and on the south west orientation than this area will require more cooling than other area in same zone.

Similarly if there are uniform heating source in area with no exposed wall at all than i prefer to take single zone since all area within same zone will have uniform cooling requirement

In Middle East or In My organization  generally they are using to split  the large  zone into multi split zone to better  heat transfer i.e to achieve cooling in very short span of time. if we considered it a single zone than it ill take  some times to feel cool  at that particular space or zone. but apart in other parts of the world they ill  not considered multi split zones except in some cases such as server room ,electrical room  and many more similar example.