The difference between the two drill bits is plane to see if you know what you are looking for.
To most observers a hole is a hole. Not so in the bridge building business. The difference in quality of performance for each drill bit is glaring. The high quality of results by using the proper drill on the right is that the hole finish is smooth and circular. The surface of a proper hole will be so smooth as to almost shine.
The single lipped $30 Irwin from the local hardware store and it's hole is on the left. The $45 two lipped 18" long Holz Master from Timber Tools does the job right. This is a big deal in the process.
Considering that the load placed on the bridge truss will be transferred though the many, many trunnels (114 per truss) in the chord and lattice web intersections. Imagine the poor performance if the holes are not round. Worse yet the surface not smooth. Over time any small fiber pieces between the trunnel and hole will be compressed and the Camber will be lost or worse the truss will sag.
Puzzler - How will we ensure the holes are drilled perpendicular to the chord surfaces?
Tech Vocab - Bushing, Drill Guide, PVC pipe, Forstner Bit