Currently, it is very unconvinient for user to fetch data of flink job unless specify sink expclitly and then fetch data from this sink via its api (e.g. write to hdfs sink, then read data from hdfs). However, most of time user just want to get the data and do whatever processing he want. So it is very necessary for flink to provide api Table#collect for this purpose.
Other apis such as Table#head, Table#print is also helpful.