It won't look as good as a monitor simply because its running a small resolution across a very large display.
For example, I connected my old Power Mac G5 to my 26" LCD HDTV at its 720p resolution which is 1366x768. Considering that a 20" Cinema Display displays 1680x1024, you can see how the Cinema display is a lot sharper.
In your case, the 720p resolution will be stretched over 62", so you'll have to sit quite a bit back to obtain the same level of sharpness, but it is acceptable for stuff like movies etc, it's just not going to be a substitute for a proper monitor.
If all you need is a cable, go for it, it's always handy to have a large TV to view movies on