In Horoscope Symbols , Robert Hand writes (concerning sesquiquadrates and semisquares):
These are not weak aspects. An exact semisquare or sesquiquadrate is more important than a square that is several degrees out, and many traditional astrologers who have ignored these so-called minor aspects have missed out on important information.
In Aspects in Astrology: A Guide to Understanding Planetary Relationships in the Horoscope , Sue Tompkins writes about how sesquiquadrates show up in accident charts, representing a kind of unavoidable energy- energy that manifests concretely . Regarding natal charts she believes that this aspect demonstrates itself through outer events rather than inner psychology because of what she sees as the tendency for these aspects to be “more deeply buried.” She goes on to say,
I suggest that the reason why semi-squares and sesquiquadrates manifest so readily in terms of outward events is simply because of the greater unconsciousness of these aspects.
Both Hand and Tompkins describe sesquiquadrates as being an energy similar in expression to the square, but less intense.