Except when you can't. I have been working with a Sony LCD television (1366x768 native) that has HDMI input and refuses to display an image using most of the EDID modes that it reports. Using gtf and cvt to create modelines is also spectacularly unsuccessful.
"720p" (1280x720) and "1080i" (1920x540) are no problem, they display (albeit badly). Text is visible during BIOS post and the TV indicates "480p", but once Grub takes over the screen goes black, even though the screen mode should be the same between the BIOS and the Grub text menu. 640x480 refuses to display at all except during BIOS post.
This is using fglrx... using the open source radeon driver results in no display at all in any mode after BIOS post.
What I'm saying is that it underlines the futility of making an EDID thread... the displays that actually have problems are ones that report false EDID information, so the results of the EDID output will be largely useless. A better idea would be for a "working modeline" thread focused on displays that are known to be problematic.