If you use PostgreSQL with jBPM, pg_largeobject table keeps increasing even after process instances are completed. In order to delete orphaned (= unused) large objects, you need to run vacuumlo tool (https://www.postgresql.org/docs/9.4/static/vacuumlo.html).
vacuumlo analyzes database to find orphaned large objects. But it only looks at 'oid' columns. In jBPM, there are 'text' columns which hold large objects. In Java codes, they are String @Lob fields which are considered as "CLOB". These 'text' columns are not analyzed so vacuumlo could delete non-orphaned (= active) large objects.