A dedicated line is a direct "homerun" line from the power panel to an outlet (at least that's what my electrician termed it), no branching or serial connections of outlet boxes. I added one in my old home in the early '90's and was underwhelmed by it - - no better, no worse, it seemed.
After a few years I had read about inductive loops in a wire, and I remembered that I had coiled up extra romex to allow for a longer placement of the line some day, should I so choose. I spent 20 minutes truncating that extra coil, and, wow! What an immediately obvious improvement! Greater clarity and microdynamic "fleshing out" of the music. An obvious improvement, without doubt. My ignorant building of an inductor for my power feed was a clear mistake.
I have implemented 10 ga. Romex in my new home's dedicated room for all outlets, and that has been my baseline for years. I tried a Topaz isolation transformer (5 kVa) inserted into my main line and it seemed to offer a mild improvement in clarity and separation of musical lines. I then wired it for balanced feed, and it seemed to offer another mild step forward.
More recently I pulled the transformer out and plugged a PS Audio P10 regenerator into the dedicated outlet and that has worked beautifully for me, even with two mono blocks plugged into it. I definitely prefer it to the transformered line alone. FWIW.