Most TVs are limited to 60 Hz except those that have dual DVI, display port or HDMI 2.0, which obviously is not an issue if the TV is just 60Hz or less anyway. In addition some TVs use technology that creates extra frames through guess work which may or may not make things look weird (especially true in fast moving games like first person shooters). ANother downside of lots of TVs is the input lag (time you press the keys/mouse before it is registered), this is not true with all TVs though.
That being said you will get a much bigger screen for your money if you go with a TV plus you will also have a TV. Personally I would only get a TV for the following reasons:
1. I couldn't afford a good TV and monitor so would just buy a TV with...