Could you elaborate on "run a very large variable separately" There are things you can do parallely and there are few things you can't(if the output of one is needed as input for the next). The stuff you can do using Parallel Computing toolbox mostly fall under the embarrassingly parallel paradigm.
This might be helpful for when to use parfor: http://www.mathworks.com/help/distcomp/getting-started-with-parfor.html#brdqg4q-1
If you can provide further information on what you are doing then I will be able to give you a clearer picture.
