It reports the same information you can find in the Apple menu / About This Mac / More Info dialog.
One of the things that makes it so useful is that you can look at the configuration of a system you are connected to remotely, like through a secure shell connection.
There are three details levels available:
- mini - report with no personal information
- basic - basic hardware and network information
- full - all available information
system_profiler -detailLevel miniIf no detail level is passed, the default level is full.
Because it generates so much information, you typically pass the output to the "less" utility, redirect it to a text file for browsing, or filter out what you are looking for using "grep".