TRMS meters generally have AC and AC+DC modes, but usually your interested in the AC portion.

** Not true.

The reason for needing a true RMS value is to predict heating in a resistance or maybe a fuse .
So you cannot omit the DC component.

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I'll bite. 99% of what I did using an AC meter was measuring power supply ripple and abcense/presence of house AC or 24 VAC systems.

When I designed an I-V converter so we could measure the outut of a UV arc lamp source, that had to be TRMS.

We had lots of phase angle fired AC controllers (before I was hired) operating into variacs to drive 40V tantalum heaters (200-300W). They either worked, had a short inside the vacuum system or blew the semiconductor fuse. I then made sure they SCR;s were 25A, added the current limit option and an extra 3AG fuse. Life got better.

New or upgraded systems went with 1200W DC power supplies. 30V 40A or so. We would have liked a power meter and a programmable temperature controller. The other controllers were obsolete. They had no temperature display and had a proprietary dual SCR unit. Newer replacements would use standard process signals like 4-20 mA 0-5, or 0-10V
That allowed us to reduce panel size and not have a "stupid panel" that read ersatz AC voltage and ersatz AC current and had a temperature display. At one point in the earlier system, Power was important. A three-phase power meter was adapted to do the power of two low voltage single phase heaters at the cost of about $1000.00 USD. There were 7 heaters in a typical system. Sometimes wired wierdly.

In a custom system (prior to the IBM PC) that I was involved in, we did it the right way. The heaters could be controlled by voltage, current, temperature or power. The uncontrolled variable became a limit. I implemented an energy calculator and stability creiteria and recipies. The energy calculator could detect a shorted thermocouple onheat up or a misplaced on, The spreadsheet programs were not invented yet.