The default restore point space allotment in Windows 7 is 1 to 3% of drive capacity. In almost all cases, the computer is using a very small proportion of the space available. That makes it very practical to raise that 3% to say 8 to 10%. This strategy will yield far more restore points that will give you much more flexibility in recovering a bad situation.
To change the allotment, type create in the text box above the start globe. Choose Create a restore point. Click configure. Move the slide to the right as much as you see fit. Setting it at 50 Gigabytes will have no affect if you have a 500 Gigabyte drive and are only using about 100 or so, which is highly typical.