Mainframe VSAM Introduction, Features, Advantages, Disadvantages IBM

You say to design the vsam record longer than the current need but that increase the need of storage. But when more space than we have is needed, we create a new vsam file with more space first and then move all the data, delete the old one and rename the new one with the same name?
Is not better to pass all the vsam data to a DB2 database, table, etc?

Thank you for this very interesting video!