Choosing a finish from a sample board is choosing it in the abstract. The colour is right in your hand and wrong in the room, the sheen behaves differently under the lighting that is actually installed, and the quantity is a number somebody estimated off a plan rather than measured off the building.
Putting the finish onto the twin removes both problems at once. The material lands on the real surface, in the real room, at its real size — and because the twin already knows that surface's area, the quantity updates the moment the choice changes rather than being recalculated by hand afterwards.
It works per room or per element, which is how refits are actually specified. A whole floor can take one specification while three rooms take another, and the model holds both without anybody maintaining a parallel schedule of exceptions that goes stale the first time somebody changes their mind.
The finishes are not a rendering trick, and this is the part that matters downstream. Each one is written onto its element as a material plus a property set, so the twin exports with every surface named and schedulable rather than merely looking correct on somebody's screen during a meeting.
That is what makes it survive the handoff to the people doing the work. Revit imports the IFC and reads the finishes as data, so a contractor pricing the job sees the same specification the owner chose, attached to the same element, rather than a description in an email that has to be interpreted.
Pricing follows from the same place. Because a line item is anchored to the element it belongs to, a cost can be traced back to the door or the wall it came from instead of to a row in a spreadsheet that nobody can reconstruct three months later when the number is challenged.
The practical effect is that a refit conversation stops being about taste in isolation. You can put two options on the same room, look at both in place, and read the quantity and cost difference immediately — which turns an argument about preference into a decision about money.
It also makes the record durable in a way a specification document is not. Two years later the surface still carries what was applied to it, who applied it, when, and what the warranty term was. That is the difference between a defect you can argue and one you simply repaint and hope.
The failure case this prevents is specific and common. Paint fails at an entryway faster than anywhere else because it is the wet part of a dry elevation, and without a record the only available move is to repaint with the same specification that failed — because nobody knows the first one was wrong for the exposure.
None of this requires a specialist or a separate tool. Materials is a mode on the same twin, so nothing is remodelled to use it, nothing is lost when you switch back out of it, and the person choosing the finish does not have to learn CAD to do it.
The habit worth building is to specify in the model rather than beside it. Anything specified beside the model has to be reconciled with the model eventually, and that reconciliation is where quantities and warranties quietly go missing.