For big battles, they look lovely. But in the quest for absolute realism of scale, where does it end?
Some would argue the board and terrain must then realistically recreate the battlefield 1:1, or the model representation is pointless. What about supply wagons and non combatants? Surely they must be represented? What about the enormous space taken up by artillery limbers behind the guns? Hardly anyone represents that exactly. Supply wagons, messengers, deserters, casualties ....
At some point you have to draw a line and say, "I'm abstracting from here on". Everyone's line is somewhere different and, as already mentioned, some people are just out to have fun with their toys and aren't looking to actually recreate anything.