It really depends...on so many factors. Many people find it a relatively low cost way to dip their toes into the world of style. Others find it a waste of time. It depends on the consultant, and also, perhaps, on your own personal colour sensitivity and awareness. Some people are literally colour blind, while others have a superb native sense of what works well on them.
I had my colours "done" before joining YLF. I wouldn't call it a complete waste, but essentially it confirmed what I already knew. I was already wearing the colours that flattered me most. I did rediscover a few that I'd been ignoring for years (perhaps because they weren't readily available.) And over time here, I narrowed my colour palette still further -- picking my best neutrals and my signature colours.
But the person who analyzed me said I had a good colour awareness already. And I would agree with that.
Where I needed more help (and did not get it) was in terms of line and cuts that flatter. Not just for broad body type (that part is pretty easy) but more -- what works with my features as well as my body to create an overall style persona?
I don't bring the little colour wallet I got when I go shopping. I have a pretty clear sense of what looks good on me already. I think if you DON'T know what looks good, getting your colours done could be fun and valuable.