I actually used to do a similar thing back in the 90's. Over the course of a project, I needed to spend about 2 weeks every month in Detroit. NW's fare SNA-DTW at the time was $1940 without a Saturday stay and $700 with. I didn't really want to spend my weekends in Detroit, so I'd book a R/T Monday to the following week's Friday SNA-DTW-SNA for $700. Then I'd book a R/T Friday to Monday DTW-SNA-DTW for $700.

Net result was 4 segments for $1400 instead of $3880. Still ridiculous of course, but better.

It was a win for me because, at the time, my company had set up a travel savings program where anytime you picked a booking that saved money, you got to pocket 20% of the savings.

Of course, it was probably an "illegal" practice then and most certainly would be now (at least on one airline).