I shoot all my own material as Progressive. About the only time I shoot interlace is when shooting airshows where the client specifies interlace, even that looks like it will change to P next year.
Interlace really is a hangover from the past where there simply wasn’t the bandwidth to broadcast full resolution (SD) progressive frames, so the compromise that is interlace was developed to split the frame into 2 half’s, transmitting one after the other. This enabled broadcaster to fit SD pictures into narrower bandwidth than would have been possible for progressive analogue broadcast. These days with most display technologies centering around progressive scanning I’m not convinced that interlace is the way to shoot. Obviously if your client insists on interlace then that’s what you must deliver.
I supply hundreds of hours of footage to broadcasters, museums and corporate production companies around the world. I have been shooting progressive since 2004. Often I deliver the material recorded as interlace, but containing progressive images. Not once has that caused me a problem. As I write this I am converting some 1920×1080 25P footage to 1920×1080 60i for delivery to NBC. If I had shot 50i that conversion would be very difficult to do and to make look good. Software standards conversion of interlace material is troublesome to say the least. It is so much easier to start of with one frame rate of P and convert to another frame rate P or I. If you start with I then you immediately have a resolution drop if you shoot with a video camera because the fields are created by using overlapping line pairs from the sensor to prevent twitter an aliasing. Converting that already resolution compromised footage to progressive will almost certainly result in a further resolution drop as you will need to do some form of de-interlace procedure. On a big screen that drop in resolution is very noticeable. Converting from P to I on the other hand has none of these issues and frame rate conversions from P to P are easy.
More and more video is ending up on the web or being delivered to computers, so for this progressive is essential. Interlace on computer screens usually looks terrible. In the future it seems likely that television broadcasting as we know it will be replaced with video served over the internet or some other data pipe such as direct to home fiber-optic, again this will almost certainly require progressive material.
More and more broadcasters are now insisting on progressive delivery of HD material, especially for documentary, drama and other high end productions. Often this is because international distribution of progressive is so much easier and the quality better. Sure 25P is not ideal, 50P would be better. But working with progressive material is so much easier than working with interlace.