Dummy load on ATX power supply

I'll get straight into the question:

Do i need to have a dummy load connected on an ATX power supply if it is going to be used as a bench power supply? Why is this dummy load needed? What happens if i do not connect it? Will it harm the power supply if it is used without the load?

Thank you very much in advance

Best Regards Dima

Many of them need to have some load current to work.

I put a small 12v lamp there.

Could you please answer the other questions as well?

ATX supply needs a minimum load on its output to regulate. If you dont have a load, the output voltages will rise above their nominal values. Depending on what the switcher chip in the supply is , the supply can shut itself down if the output voltage goes high. Depending on the power rating of the supply, you will have to experiment to find out what minimum load is needed.