You don't have to warn about things that happen rarely, not for things whose costs are already closely tracked. The point of warning about meetings is that they happen too often and go on too long.
My point is on the uncultured lowly employees who don't understand the costs of running a business: indeed, if they only knew who the most expensive employee was (by a long margin).
I actually tried to get this implemented at a startup I worked at a long time ago. We were building a new office and I tried to get the cost of meetings in progress implemented on the digital door signs because half the directors and VPs spent all their time in meetings. It got shot down by the COO because I'm sure he would have been embarrassed at the price of our exec groups meetings, but I didn't care.. we spent way to f'ing long in meetings and not enough time building things. Many did, from the kids fresh out of art school to the MBAs running go to market.
As I said, a lot of staff just don't have a sense of how much things actually cost... but I did, I was partly responsible for making sure hundreds and hundreds of people still had a job a year down the line and, myself and the rest of the over paid exec team included.