Good point, however, I'm pretty sure a C-340 is certified exclusively for single pilot operations. Although, I was wrong once.
I think that the point is that the 135 regs (IFR passenger carrying, anyway) requires two pilots, regardless of what the airplane is certified for. In 135 ops an SIC is a legitimate required crew member. Still probably not very valuable time in the overall picture, but when someone is trying to scrape together every tenth of an hour of twin time they can....
(By the way, people often talk about the 135/SIC/single-pilot-with-autopilot rules in a back-wards way, saying that ops specs allow a company to operate with an SIC. In reality the 135 rules say that you
must use two pilots for passenger carrying IFR ops, but many companies have ops specs
exemptions that allow them to fly with a single pilot with an approved autopilot. Kind of a nit-picky point, but it comes in handy in some circumstances.
For example, in my last 135 (piston twin) job we had the exemption that allowed single pilot ops. We had some customers that wanted two pilots on board for their flights, and because the 135 regs say that two are
required but the ops specs
allow (allow, not require) us to operate with only one, it was perfectly legitimate for us to log PIC/SIC time for those flights. Just because we
could operate single pilot didn't mean we
had to, and since the SIC is required by 135 regs it is perfectly legitimate, loggable SIC time.)