Diode lasers (DLs) serve as adjunctive therapies in periodontitis treatment, leveraging bactericidal, ablative, and biostimulatory effects. Numerous studies support the beneficial clinical effects of DLs in periodontal treatment, but other studies suggest that laser therapy offers no additional advantages over traditional periodontal treatments. This article provides a narrative review of the therapeutic effects and applications of DLs in periodontal disease, systematically introducing the mechanisms of action of lasers and the impact of different parameters on treatment outcomes. Photobiomodulation therapy (PBMT) using DLs has been shown to have short-term clinical benefits for periodontitis. Its mechanisms of action may be related to the antibacterial, anti-inflammatory effects of the laser and the promotion of periodontal tissue regeneration. The effectiveness of using lasers in periodontal treatment remains controversial, possibly due to the lack of standardized laser usage guidelines in each clinical application.