Image quality, perspective control and the ability to fine tune or CONTROL every step in the process.
It is also the only photography as slow as my wife sketches or does water color. A mutual appreciation and enjoyment of visual arts together cuts w-a-y back on the complaint I hear in many ULF marriages, "Why don't we do anything together?"
I ask my husband that same question. However, I am the one doing the ULF photography, not him.