You should read some basics of relation algebra:
cartesian product means that every record of Table A is joined with every other record of Tbale B so you get expotentially resultsets:
Table A | Table B | Reultset
100 | 100 | 10000
1000 | 1000 | 1000000
and so on and so on...
you can figure out that this gets big really fast, that why there is something like Max_Cartesian_Result.
regards
dj