If the size of a large object is less than the value of this property, all the dataof this large object are placed to a single INSERT statement. Otherwise, PgSqlDump reads the large object data in parts of the BlockSize size and generates a separate statement for each part.
If your large objects are not too big, it is better to keep the default value. For bigger large objects it is better to dump data into several statements with less data than in one huge statement, because such statement can cause insufficient memory errors.
Note that decreasing BlockSize value causes increasing the number of round-trips to the server and longer dump duration.
We recommend the values for this property from 64Kb to 1Mb.