Lids on tanks????

[supersmile]

What is your opinion about having a lid on your tank? I have had a few people say for sure get a lid because fish jump. Others have said a lid mucks up with the temp of your water and isn't good. As well some people say they haven't had a lid on their tank and nothing ever jumps out. I am a bit confused on what to do. I heard of people using that plastic stuff that you can get from Rona etc that comes in a plastic sheet and it is composed of little squares which enables the water temp to regulate?????