synastry

I was wondering, what are the effects of different venus/mars aspects when comparing two charts to assess a relationship? That is, what effect might a person's venus conjuncting another person's mars have? Or venus trining another person's mars? What about if the two are sextile, square, or...

What else in the chart would overcome it or how to handle it

Do you find it useful, or is it better to just compare two charts the normal way? Or are both ways of equal use?