I believe the biggest difference is that a SELECT statement retrieves from the database and the LOAD statement has to do with how it is loaded into QV's memory. I am sure there is more to it.
LOAD is usually used to load from a qvd, from an Excel - anything except a database, actually
<=> You can, and should probably, use a LOAD on top of a SELECT when you load data from a database (because some functions might be available in QlikView which are not part of the SQL syntax and v.v.).
