Here is why I recommend leaving it on auto...
 
Should you get involved in managing the page file? If you have more than one physical disk, moving the page file to a fast drive that doesn’t contain your Windows system files is a good idea. Using multiple page files split over two or more physical disks is an even better idea, because your disk controller can process mul¬tiple requests to read or write data concurrently. But don’t make the mistake of creating two or more page files using multiple volumes on a single physical disk. If, for example, you have a single hard disk that contains volumes C, D, and E, splitting the page file over two or more of these volumes, might actually make your computer run more slowly. 

If you are short of hard disk space, you might consider setting a smaller initial page file size. Monitor peak usage levels over time; if the peak is well below the current page file size, you can consider reducing the initial size to save disk space. On the other hand, if you’re not short of disk space, there’s nothing to be gained from doing this and you might occasion¬ally overload your custom settings, thereby degrading the performance of your system. 

Should you enlarge your page file? Most users won’t need to do this. But you might want to keep an eye on the green line in the Memory chart on the Overview tab of Resource Monitor. If that line is spiking off the top of the graph a great deal of the time during your normal work, you might consider increasing the maximum size of your page file. (Note that you should disregard page file spikes and disk activity in general that takes place while you’re not actually working. This is likely to be the result of search indexing, defragmentation, or other background processes and does not indicate a problem with your actual work performance. 
 
https://technet.microsoft.com/en-us/library/ff382717.aspx
 
 
Another good read: http://azius.com/blog/pagefile-yes1/