Lossless codecs such as UTVideo and Lagarith are not intended for normal playback, and as such you probably will not get reasonable results trying to open them in something like MPC-HC. However, for editing purposes I have never had trouble with them as far as playback speed goes, even on my old Pentium D e5200.
In regards to comparing lossy codecs to lossless for editing, one of the most important benefits comes from intra-frame compression: lossless codecs like the ones mentioned above store complete frame information for every frame, whereas lossy codecs most often use keyframes at set intervals, and between them only the changes in picture from the previous frame are stored. Practically, this means that if you try to seek backwards with lossy codecs it is likely that you will get mixed, often inaccurate results.
For a fun test, try opening some footage encoded with UTVideo in VirtualDub. If everything is configured properly, it should have no trouble playing the footage back in realtime. You should also be able to randomly jump to any part of the footage without delay or image quality problems.
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