Cathepsin L inhibitor III is primarily used in research to study the role of cathepsin L in various biological processes. It is particularly valuable in understanding the enzyme's involvement in cancer progression, as cathepsin L is known to contribute to tumor invasion and metastasis. By inhibiting this enzyme, researchers can investigate its impact on cellular mechanisms and potential therapeutic targets. Additionally, it is used in studies related to viral infections, as cathepsin L plays a role in the processing of viral proteins. This inhibitor also aids in exploring the enzyme's function in autophagy and lysosomal degradation pathways, providing insights into cellular homeostasis and disease mechanisms.