One of the most common pieces of advice about cutting vinyl that we see online or get asked is that the low end has to be mono. It’s often treated as a rule, but really it’s a practical thing rather than a requirement.
The reason low frequencies are often summed to mono comes down to how stereo is physically cut into a record. Stereo information is cut as vertical movement and at very low frequencies, wide or out of phase audio can cause large vertical movements. These movements make the groove harder to cut cleanly, in severe cases lift the head breaking the groove. Summing the bass to mono reduces that vertical motion, keeps the groove more stable and makes cutting easier, especially if cutting long sides and disc space is essential.
That said, monoing the low end isn't about getting a better sound, it can be the opposite, it’s about controlling vertical movement. If the low frequencies in a mix are already under control and in phase there’s often no technical reason to put them to mono. Many mixes naturally have centred bass and when phase coherence is good, those low frequencies won’t cause issues with vertical movement in the groove.
There are also musical reasons not to apply an elliptical filter by default. Some material relies on subtle low end or low mid stereo information for width or movement, and summing it to mono can change the feel of the mix in a way that isn’t always good. Also, when using an elliptical filter people often mono way too high, for example set to 200hz but depending on filter settings the crossover frequency can affect audio up to 400hz, which is obviously not intentional.
Basically, monoing the low end is as a tool, not a default setting for each cut. The goal is always groove stability and reliable playback. If the bass is phase coherent and the groove remains stable there’s no need to force it to mono. As with most areas of cutting, the best thing is to understand why the technique exists and then decide whether it’s actually needed, often it isn't.