With shared hosting, you are on the same server as several other sites. his allows the host to keep costs down. This is ideal if your site does not have a lot of traffic.
If you run a resource-intensive site that generates a lot of traffic you really should be running on a dedicated server because you will have total control over the use of the server's resources. Having root access will allow you to perform custom program configurations and monitor the usage of server resources so you can identify any potential issues.