It's a fairly common practice to set the SQL Server Services (Engine, Agent, OLAP, RS, etc.) to automatically start when the server does. But is this a good idea?
I don't set my services to start automatically. If the server is unexpectedly rebooted, I want to know why before I start SQL Server. Sure, it's begging for a 2 A.M. call on the pager system, but if you really care about the data, it's worth knowing that the server was shut down without your knowledge. If the server, or even worse, the database, has an issue and the system is restarted, you could actually do damage to the data - rare, but possible.
So I guess it's a judgment call - if you're OK with the database restarting without your intervention, set the services (in Configuration Manager only, please) to start automatically. If you're paranoid like me (and many DBAs are) then set them to manual.