When replicating in this type of environment, it is important for the data receiver to send an acknowledgment message after receiving data changes as often as possible. If no acknowledgment messages are received, the data sender resends changes and maintains the information needed to resend changes until those changes are acknowledged. As a result, the data sender's geodatabase can become large and new data change messages can also become large.
As the above statement mentions, the Data sender will resend the changes till those changes are acknowledged.
As a result, the data sender's geodatabase can become large and new data change messages can also become large.
This part is not because of the previous statement. This is just indicating that as and when the data in the Data Sender geodatabase keeps on increasing with time, the new data change messages will also keep becoming larger, because the previously sent change messages have not been acknowledged yet and the data sender gdb is sending all changes.