Sure. In many places, it is now code as I understand it.
Copper is a better conductor than steel, and it probably has much more static volume, which is one reason you changed things out. While the old pipes and the new may have had the same volume when new, the old galvanized pipes only had a small inside diameter after many years, so the system didn't have to fill it up with hot water.
In between uses, the hot water in the pipes will cool off - it did it with the old ones too. But, there is more of it now, so it takes longer for it to be purged with hot from the heater before it gets to you. If you have long intervals between hot water uses, the insulation won't help much. But, in between, if it is insulated, it won't cool off as fast.