75° is the point halfway between a sextile and a square. The 105° distance is halfway between a square and a trine. By being halfway between, these points mark the WEAKEST aspect connection between planets: Aspect connection peaks at greatest strength at certain points like 60°, 90°, and 120° and is weakest between.
While it would be theoretically possible to contrive a meaningful interpretation based on a kind of "anti-aspect" relationship, the normal thing to do is just ignore it. That is, if one had Sun and Jupiter 75° apart, one could say that this person had the least Sun-Jupiter traits anyone would every have
unless something else in the chart showed similar traits. Considering how much stuff we already find in a horoscope, a subtlety like this is likely to get lost in the mix.
For example, I have Mercury and Pluto 75°15' apart. Giving by this alone, you would expect Pluto would have less impact on my Mercury than for 99% of all people everywhere; however, how do you interpret this? And the "no Mercury-Pluto connection" is lost since I have two strong midpoint connections, Me=Ju/Pl and Me=Ur/Pl that give more than a little of a Mercury-Pluto feel on their own.
For some specialized purposes (like sunspot prediction), a few researchers have found micro-harmonics important, such as the 24th harmonic (an "aspect" every 15°). This would include the 75 and 105 distances; but these micro-harmonics don't seem to penetrate into natal astrology.
Bottom line: These are as not-aspects as one can get