S_(N)1 reactions are important because, as far as we know, they describe a mechanism of organic reactivity, of chemical reactivity. And they describe a BOND-BREAKING PROCESS, as compared to S_(N)2 reactions, which are bond-making processes with respect to the rate determining step.
S_(N)1 reactions are characterized by the loss of stereochemical activity. That is for CR_1R_2R_3X, substitution results in the loss of chirality, due to a presumed ""^+CR_1R_2R_3 intermediate.