A restart may be necessary if the phone is a Symbian Anna or Belle based phone. If you wish to hide the super SU icon that appears during installation, a respiring becomes imperative for all iPhones as well as for some rooted Android phones. Given below is a short recap.
For iPhone, a restart (respiring) is required once after the completion of installation
For Android, if you choose to hide the SuperSU icon, then a restart is required for some rooted devices.
For Blackberry no restart is required.