One possible clue for running gel electrophoresis  at lower temperatures is that if you are running gels with less percentage of agarose in them for longer period of time your gel might end up melting due to heat generated due to current flow.

Second good reason for running gels in low temperatures is to slow down the activity of nucleases (DNase/RNase) contaminants to avoid breakage of your target DNA/RNA being resolved in the gel.

The bands obtained on lower temperature will be more compact less diffused in the gel.

Hi Dr. Jeffry

                     Temperature plays a bit role in electrophoresis. With decreasing the temperature your band become more dense or neatly packed in gel. You can check this attachment , this is showing the AGE of same protein at various temperature (Increasing temperature from the marker side).

Hi Dr. Jeffry

As explained by Mr.Abdul and Mr. Bharat, the basic reason to run a gel in cold is to avoid the overheating of buffer, which usually occurs when one runs the gel at high voltage. Specifically the low melting agarose gel is usually run at low voltage and at low temperature to get intact band and clear resolution of band. As we can see in the above attachment, the gel run at higher temperature lead to smearing of band.

Kunwar and Ryan,  Thank you for your replies.  They are very helpful.  - Jeff