Is that really the best tool for driving lag bolts and spade bits?
Nope. In fact, lets quote the manual for the product:
"These impact drivers are designed for professional impact
screwdriving applications. The impact function makes this
tool particularly useful for driving fasteners in wood, metal
and concrete."
Looking at the DCD791, a drill often paired with the DCF887:
These drills/drivers/hammerdrills are designed
for professional drilling, percussion drilling and
screwdriving applications.
Spade bit = drilling, so it is an incorrect use of the tool. I would expect the impact driver to be able to handle it occasionally, but not for nonstop use. I would also throw out there that the bits being used may not have been impact rated. The whole video seems like a bunch of people acting shocked when their 1/4" drive HF socket breaks when a six foot breaker bar is applied to it.