Many people said the Rega tonearm matches well with the denon 103rI have found this to be not true, at least to my ears. I suspect that the DL-103x gets used in these situations mainly because they are one of the, if not the, least expensive MC cartridges on the market.
In a nutshell, a compliance mismatch will result in less than optimal sound (duh!). This can include the system sounding overly bright or dull and lifeless, depending on if the cartridge is over or under-damped by the tonearm. What is less understood is that a severe compliance mismatch can also result in poor stylus tracking and a smeared or "inaccurate" soundstage presentation.