Yes. In terms of cruise this difference, time wise' between M0.78 and M0.80 is very little on 2-3 hour sector. You may save 2-3 minutes but you will burn A LOT more fuel. Additionally, when you arrive at destination you may have to hold (in the air or on the ground) so any time made up is lost.
The place you really make up time if delayed is on the ground. If you really "drive" the turn around you may save possibly 10 minutes - for free.
The other risk of flying round on the barbers pole is that of a possible Overspeed due to turbulence or positive sheer.
Most companies are very focused on fuel at the moment for obvious reasons. Chucking an extra $200 worth out the back to
maybe gain 2 minutes just isn't worth it - especially if your airline does >1000 sectors each day. It's why I'm always surprised that a particular very large low cost carrier seems to dash around at 320knots / 0.80-81 much of the time. Companies have SOP's and if they want us to fly ECON I'll do it - after all it just makes my available 900 annual hours get used up quicker
A4