It was important because there were specific job requirements that had to be met in order to qualify for a TN visa. The expertise you were expected to be bringing in as a Software Engineer was architectural level knowledge of coding.

The TN visa could be revoked at any time which is why you want to be really clear when crossing the border. I worked for Microsoft and they recommended that I bring my full job description package and lawyer's letter every time I crossed the border

The best part was when I had to go to the border to apply for the TN visa. The poor guy had a list of questions to ask and clearly had no idea what any of it meant. "And will you be doing any <...long, dramatic pause> programming?"