You will want to keep the OS on the SSD. Everyone here will drop to their knees and cry if you don't.
So that leads to the question: how big is the SSD and what do you have on it?
What most folks do, particularly when using a small-ish SSD, is install only the OS and maybe a few hard drive hungry, high end programs or games on it. They then install all other programs and all of their user files on the "spinner".
To free up space you could uninstall programs one at a time and reinstall them on the spinner. User files can be cut and paste. And you can redirect the default "My Documents" folder to the other drive too.
Hope that helps.
My Computer
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Home Built - Jan 2013
OS
Windows 7 64 Bit Home Premium SP1
CPU
i7-3820
Motherboard
Asus P9X79-PRO - Bios 4608
Memory
GSkill F3-14900CL9Q - 16GB
Graphics Card(s)
EVGA GeForce GTX660 - Driver 352.86
Sound Card
On board Realtek ALC898
Monitor(s) Displays
Acer S271HL
Screen Resolution
1920 x 1080
Hard Drives
#1- Samsung 840 Pro Series
#2- Western Digital WD1002FAEX Sata3 Black
#3- Western Digital WD1002FAEX Sata3 Black
PSU
Corsair CMPSU-850TX-V2 - 850 watt (by Seasonic)
Case
Corsair Obsidian 550D
Cooling
Standard 3 120mm case fans, Cooler Master Hyper 212 EVO
I have World of Warcraft on it ( lol )
And a couple other games, so if I just start installing things on my HD and uninstall whats on my SDD (what I don't need on there) I should be a ok...right?
From what I know, WoW takes up a ton of space, and should have been installed to the data drive in the first place. When I used a small SSD, I had it as my C drive. I had a 1 TB HDD as my D drive (I moved drive letters around to make my optical drive E. I created a folder on D called Games and installed all of my games there, rather than put them on the SSD.
So, to make a long story short, you should be able to uninstall, then reinstall your games, such as WoW, to your data drive.