I am wanting to buy a splitter for my cable television line to enable me to use Picture In Picture and record a channel while watching another. I am wondering how this effects the quality of the picture. At what point does dB loss become visible, and what would be a good dB threshold to stay above for each split signal? For the purpose of splitting the signal right at the television with comparatively short length coaxial cables, is there a need to buy an In-Line Amplifier (Signal Booster), or is it safe to just go with a signal splitter by itself?

I'd say it varies from location to location, so you'll have to try it and see. Here, I was ok splitting it into two, but splitting it into four required buying an amp/splitter that gave each branch a 3dB boost. Otherwise I had mad snow.