Your Typical Compression

[Qyot27]

Since what Streicher said was specifically about H.264, CABAC is very CPU-intensive, and the higher the bitrate=the more CABAC has to compress=the more CPU power needed to handle the video. Yes, resolution exacerbates the situation because larger images need higher bitrates to enable them to look better as well as the demands on the amount of screen area to decode to, but two different H.264 encodes at the same resolution and without anything fancy like softsubs can take drastically different amounts of CPU power to playback depending entirely on bitrate. It's readily obvious when comparing one video that has a bitrate ≤ 1000kbps and one with a bitrate ≥ 2000kbps (which unless the source is absolutely piss-poor or extremely high-motion, is unnecessary for an H.264 encode when talking about 480 or less pixel height aspect ratios), especially when using ffdshow and comparing them on machines which would not have enough power to play both of them effectively (1000kbps may play perfectly, while 2000kbps lags like hell), although the CPU discrepancy would still appear regardless of processor strength, even if it may not be as big of a discrepancy on more capable machines or ones that have H.264 decoding ability in their graphics card.

Also, the demands of playing back two H.264 encodes at the same resolution and same bitrate, but where one uses CABAC and one uses CAVLC (which is what gets defaulted to when CABAC is disabled), will also show this discrepancy.

[Keeper of Hellfire]

One video I did, I made an XviD version and a WMV version, and they both looked exactly the same in terms of visual and sound quality, the XviD version was just at a lower resolution and took up more (a ridiculous amount) of file space, which is completely unnecessary.

In one point you are right, if it comes to hard compression, WMV9 (!, not WMV in general) performs better than XviD because it's imitating some h.264 properties. But the point ist, the visual quality isn't good at all if this point is reachead. If you want a result that I define as good quality, than WMV9 and XviD have pretty well the same bitrates. And if I use a different player than WMP, XviD needs less playback power than WMV9, so it can be played at much weaker machines. And since when are WMV and XviD audio codecs? WMA is the audio codec, and the companion of XviD is usually MP3. And yes, WMA can compress harder than MP3 for the same audio quality.

Probably this explains all:

...so why would I waste my time when I can just import it into WMM, and save it as a WMV...

You should immediatly visit an optician. None of the WMM standard WMV encodes looks good.