Protein after translation can have several modifications, they are called post-translational modifications. It could be: addition of peptidic or lipidic products, it could be acetylation, ubiquitinylation, methylation, oxidation or glycation.... or it could be protein cleavage.
CLEAVAGE:
It could be the elimination of the N-terminal methionine
It could be a maturation of the protein by cleaving a portion of it. It could be intracellular like insulin, or extracellular like pepsinogen
It could be a cleavage for the deactivation of the protein.