Lots of lore in audio @holmz.
It is inaccurate to say there is no benefit of a dedicated line in all installations. It will significantly reduce the impact of high instantaneous draw sources (dimmers, etc.) by putting them a different AC run. If it is on the same run, you are exposed to the the instantaneous drops on that run. If it is on a different run, those drops are buffered by the incoming feed, and filtered by the inductance of the dedicated run. Value depends on how susceptible your equipment is.
If a high current dedicated run allows you to plug everything into a single outlet box sharing the same ground as opposed to multiple outlets, that is a benefit as well. About the worst thing you can do is multiple runs and multiple outlets. I have seen that suggestion often on audio forums. It is a bad idea.
Noise does couple from line and neutral currents into ground and that can also generate noise in your system. A dedicated run with better wire, not expensive, just better will help for this.
As always, YMMV. Your electrician is not right or wrong. Don't assume you have a noise issue. If you play something analog or digital and cannot hear noise in quiet passages (silent sections), then it is highly unlikely you have a noise issue. There is a slight chance that noise could create more jitter if you are using a coax digital cable. If you are worried about that, get a better DAC. For analog, the noise in the silent parts is everything.