Go with SCH if:

1) You want to run low level content without actually healing at all and just being a DPS with a healing pet.
2) You want to LVL SMN but don't want to actually use SMN until you have Bahamut (my main reason for leveling SCH to 70).
3) You have to be busier than a WHM but less busy than an AST, due to having to kind of micro manage pet but not really.
4) You like pet jobs.