From the ECFMG: Asking for a Letter of Recommendation (LoR)
Source: ECFMG Strong, comprehensive letters of recommendation (LoRs) can provide you with an extra edge when competing for a U.S. residency position. Residency programs have a limited number of interview slots, so they need to screen a large applicant pool carefully to select only the most promising candidates. Good LoRs may be a deciding factor[…]