For the very small amount of oil that's trapped in the cooler, pulling the lines on and off may cause seepage issues down the road. I do check the tightness of the hose clamps on my cooler at every oil change but pulling the lines off is a little overkill in my opinion.

 

I would not remove those oil lines from the cooler. You are asking for a drip in the future.The small amount of oil in the filter will mix just fine with the fresh.

 

I would not pull the oil lines.
There are products out there that "pump" the oil through thereby getting almost all the old oil out. Personnally I don't work about a few ounces of old oil left in the system.

 

I agree, 8 ounces or so of oil is of no concern. I'm sure there's a few ounces here and there in the motor also that don't get out with a drain, so just one of those things.

Now my Horizontal Jagg oil cooler does drain naturally due to it's orientation, so one advantage to the horizontal cooler - the oil runs right out of it as both lines go in and out from the lower end.

But yes, disconnecting the hoses is probably gonna cause you seepage problems that's just not worth the few ounces in the cooler.