The cycle time is too long for sensitive items like butter. Even at low power it will bubble over before it fully melts.

In addition to everything else people mentioned, high power microwaves tend to cause pockets of steam inside food which explode and make a big mess all over the interior. By dialing down the power level on an inverter microwave, you eliminate the chance of that happening. This did not always work on the old cycling microwaves due to the long duty cycle.

Anecdotally it seems to heat much more evenly, without the lava and ice pockets my old microwave left.

Excellent for things like melting butter or chocolate

Seems to work better for defrosting evenly without risking cooking the item, which is one of my main use-cases for a microwave.