EAD Vs H1
When you switch to EAD(using I9) your H1 automatically expires,
With H1 you also have the ability to travel (ofcourse you need a stamping on your PP)But unlike H1, EAD has absolutely no restrictions as to which employer you can work for and how much salary you can earn ( except for the expiry date.)
Unless you need to change Employer after 180 days of filing 485
or your GC sposoring employer is unwilling to renew H1 , EAD is not necessary.
Most people apply for a EAD as a safety precaution incase they loose job. Just having a EAD does not cancel your H1 !