Saturn aspects in synastry are notoriously difficult to handle. Saturn represents depression, restriction, fear of rejection, distancing, as well as commitment. Saturn aspects are certainly binding, but come with many problems. Here are some descriptions of how hard aspects (i.e. the conjunction, square and opposition) from one person's Saturn to another's Sun, Moon, Mercury, Venus and Mars manifest in synastry.
Saturn Square Ascendant
This combination indicates conflict over professional, martial and personal affairs. The Saturn person will be a restraining and disciplining influence on the Ascendant person but they may resent this restriction and see it as a threat to freedom of self-expression. The Saturn person will resent the Ascendant persons tendency to act impulsively without proper mutual planning. This can lead to coldness and emotional distance in the relationship.