Here's some info from this link
The Problem with Interlacing: Screen Size
For most of the 50 years that the plain ole "525i" television has been in existence, it has worked just fine. That's because TVs were small. On a 19" TV set the picture looks great because the scan lines and the errors introduced by interlacing are too small to see. But as TVs have gotten larger, the scan lines have become more visible.
Not only that, but the interlacing system creates weird "artifacts" when blown up to big-screen proportions. When there is motion in the picture, an object will have moved between the time the first half and the second half of the frame are recorded by the video camera. That makes straight lines break up and look like they've got jagged edges. And on a 60" TV or a genuine large-screen image from a front projector, the visible scan lines and jaggies can be enough to drive you nuts. Many will remember the very poor picture quality from the earlier generation big-screen TVs—if you sat too close to them you'd go blind in a hurry.
The fact is that the 525-line interlaced system we have today was invented in 1953 when televisions were small. The picture was never designed to be blown up to large screen proportions. What works beautifully at 19" is a disaster at 60". And TV designers and marketers know that they couldn't continue to sell really bad video forever just on the WOW factor of the screen size. So they came up with ways to clean up the picture.
The New Solutions
The single largest step that was taken toward better big-screen video is to eliminate the interlacing. Interlacing was originally invented to save transmission bandwidth, since with an interlaced signal you only need to send half the frame (either the even lines or the odd lines) at a time. But now we have media such as DVD from which we can read and transmit picture information much faster than ever before. So there is no need to stay with an interlaced format.
The alternative to the interlaced presentation of the odd and even numbered lines is a process called progressive scanning. Progressive scanning simply means that all of the lines in the frame of video are painted onto the screen in sequential order from 1, 2, 3, 4, . . . up to 480 in one pass. This has the potential to give us a cleaner and more stable picture. However, the video signals are still being broadcast in interlaced format, half the frame information at a time. So the frames need to be assembled into full 480-line frames before they can be painted progressively on the screen. This process is commonly referred to as deinterlacing or line doubling (more on this in a minute). This 480-line progressive scan technique is commonly referred to as 480p. However, there is still the interframe gap, and there are still 525 total lines. So some people call it 525p instead of 480p. But it's basically the same thing.
Of course the marketers needed to come up with a snazzy name for this simple new concept. So they did—Enhanced Definition Television, or EDTV.
EDTV is a major advance
EDTV, or 480p, doesn't sound like much compared to HDTV. But it is in fact a major step forward in picture quality. On a big screen it looks closer in quality to HDTV than it does regular television. And it is here today. Most DVD players on the market output both interlaced and progressive signals, and they are getting better and cheaper by the month. (At the moment, the Costco down the street is selling a little progressive scan DVD player for $79.99). That means that every DVD movie and video on the market can be played in EDTV right now.
So here is your first absolute rule for buying a new video display, whether it is a projector or a TV: make sure that it is 480p compatible.
But, you ask, what about regular interlaced video sources like cable television, VCR, and so on—how do I play those signals on a progressive scan video system?
Well, no problem. You simply feed your new projector or TV the interlaced signal just as you always did with your regular TV or VCR. All of the newest video systems will accept interlaced signals as well as progressive. They can do this because they have a device on board called a deinterlacer or line doubler.