Shutdown vs. Sleep is a constant question.
It used to be that shutting down the early OS X machines caused issues with timed log cleanup routines. That's pretty much a non-issue these days as the OS recognizes when the routines haven't run and will reschedule them.
Another concern has been restarting to free up memory or just make the machine more stable. This has been overcome to a degree by the sandboxing of apps so that they don't intrude on each other's memory footprint, etc.
The other big consideration is cost. Apple does a good job of making sleep efficient, but it is still uses 4x-5x more power than shutdown (also known as idle). This is dependent on your Mac (iMac = 4x and Mac Mini = 5x).
You can read more about this on Apple's site and select the report for your Mac.
Also, shutting down a Mac still causes some power drain and is referred to as "idle" by Apple. Consider that it always needs power because you can set your Mac to automatically shutdown at a certain time and startup at a certain time (System Preferences > Energy Saver > Schedule). For me, I set automated sleep and wake times and almost never reboot.