I use flash meters extensively, both for balancing multiple strobes and for manual strobe fill.
I use spot meters extensively with LF.
I use the incident meter any time I suspect the values I've metered with the reflective meter.
Currently my favorite meter is the Sekonic L-508, which performs all these functions.
I also have a small metering "wand" intended for the Minolta meters, but it works just fine on the Sekonic. This is invaluable for working in small spaces, especially for macro.
When using any TTL system, I always use the 508 alongside it and compare results. If there's a big disagreement, it is a nudge to figure out why, often saving me from metering mistakes in critical situations.