Most OD trans have lock up converters. Now there is the issue that it takes some of the fluid from the clutch packs to lock the converter up. (So I have been lead to understand). I have not seen this as being a problem in the installs that I have done. I'm not a transmission guy, but I am assuming because the converter is only locked once the trans is in OD, you're not stressing the clutch packs as much (?).