It depends on the family member, and on whether all the forms are accurately completed at the time.
For example, some people want to sponsor a cousin - that's quite unlikely to ever be an option. Some people might want to sponsor their parents - for which they'd need to wait years, have proof of income, and get lucky in the sponsorship lottery. Some people might want to sponsor their spouse - so the spouse would need to be properly declared as non-accompanying during the original application, and if they had not been then they would be permanently excluded from family class sponsorship. Etc etc etc.