Matching the level of your track and the reference helps you determine how they stack up, as our brains are just trained to think “louder is better” oftentimes. You can go either way with it, but the move is usually to bring down the reference track to your mix’s volume. Essentially, you want to make the elements of your mix sound as close as possible to the reference in terms of tone/balance/etc. at the same volume, because then it’ll sound right when you do get up to commercial levels. Also, like James mentions, it gives you targets to shoot for in terms of sound/vibe/etc. For example, if you were trying to make your quieter mix have a low end as loud the reference track at its normal volume, you’d probably do drastic, unneeded EQ or volume moves that’d ruin your mix when you tried to balance and bring in other elements. Reference plugins usually have a volume match option, so they may be worth looking into. I use Metric AB, but I know a lot of folks on here swear by Reference. Using YouLean to separately get the levels of your mix and the reference and then volume match appropriately is definitely a good, free option. Good luck! Soon as you get the hang of using them, it’s an invaluable skill 🤘🤘