From the Introduction:
Sefer Shimush Tehillim is a short and relatively little-known treatise attributed to Rav Hai Gaon (according to the Sedei Chemed) which describes the Kabbalistic uses of particular chapters and verses from the Book of Psalms for prophylactic or healing purposes. These selections are meant to be either recited alone, frequently multiple times, or in conjunction with some other action or prayer. Shimush Tehillim is mentioned in Teshuvas HaRashba (413), by the Chida, and others. This work is not to be confused with bibliomancy which is the use of Biblical verses for predicting the future.We attend a synagogue where an additional Psalm is recited every weekday after Minhah on behalf of something. We believe that is an overuse and misuse of Tehillim.