SysQuery::countTotal vs SysQuery::countLoops

Why sometime I have to use SysQuery::countTotal and sometime SysQuery::countLoops

and the result is not the same.

EX:

conteur=   SysQuery::countTotal(inventtable_ds.queryRun())  ;

conteur=   SysQuery::countLoops(inventtable_ds.queryRun())  ;

Thanks