Yes, it's important.

You want to be sure your really getting rakeback when you sign up for a cardroom.  There are a lot of sites that will tell you your getting rakeback when your not.  They dress up the rooms VIP program and call it RB, I call this "putting lipstick on pigs"  You see RB is a program with very few strings attached, VIP programs have all kinds of strings attached, in fact many players never get anything out of VIP programs because of the bull!

When you see a site offering RB on a room that does not have RB, run from that site!

For example Merge Network rooms quit offering RB a while back but you will still see sites offering RB on Merge rooms.  Either they have not updated there site since Merge ended RB or they are being very deceptive.  In any case such sites should be avoided!

Rakeback is simply a rebate or cash back on the rake you have to to a particular poker site.  Rakeback is free to sign up for and can be brokered through deals with poker affiliates or the individual online poker room's management.  In some cases, rakeback is paid daily back into the player's account.  In most cases, it is paid weekly or monthly through rakeback affiliates who have plenty of cash out options.

Rakeback is basically free money and there is no catch.  It is simply a rebate on the rake you have to paid to the poker room.  Online poker rooms will calculate rakeback differently.  The shared rakeback method divides rakeback amongst all players who were dealt into the hand.  The other method, contributed rakeback, players must contribute to the pot to receive rakeback.  One last note on Rakeback, users signed up for rakeback may not be eligable for VIP programs or certain promotions if they are receiving rakeback.  Rakeback can be extremely profitable and is something everyone playing poker online should look into.