OK, lets back up-
Trevor, actually the Mixcraft master meters last "marked" increment is -6Dbfs, but zero would be here:
But the reason I would use something more precise (for the purposes you describe) is that you cannot judge peaks by eye, as you would never see it and this type of meter just doesn't accurately show it anyway.
Even some meters that have peak indicators many times miss by a little. There's often a difference between common peak meters and "true peak" meters.
And, often mix downs or masters that were set to 0 peak can be analyzed and show some clipped peaks for various technical reasons beyond potential metering errors anyway.
These are but some of the reasons many engineers consider working at the edge of 0 to be a poor choice due to the fact that DA converters don't work as accurately when you get too close. Most recommend slightly under for wav, and a minimum of 1 dB under for MP3's
So unless one is intent on absolute loudness at all costs..... That isn't something I do anyway.
And as far as the VU meter thing goes, (I strongly suspect you know some of this, but some other reader may not, so):
The VU meter was a reference in the analog days, and referred to a level centered around what is equiv. to about -18dBfs (dBfs being a completely different digital reference scale), and the old VU scale isn't equipped nor intended to give any peak reference. Its an averaging thing.
Being old school I initially found familiarity in using a emulated VU meter for some purposes, but I have gotten over it and moved into the modern times.