Park Tool DP-1 Dummy Pedal
Many new bikes do not include pedals. The DP-1 Dummy Pedal quickly installs to take the place of a pedal when making adjustments during the assembly of these bikes. Use of the DP-1 is much quicker than threading a pedal into the crank and then unthreading it after the bike is assembled.
I have never worked on a bike where I needed a dummy pedal. If for some reason, I need something to hold onto besides the crank, then I would install a pedal. When adjusting braking and shifting, though, gripping the crank is sufficient.