One of the most common things you want to do for a feature flag or metric name is ask, "Where is this used in code?". (LaunchDarkly even has a product feature that does this, called "Code References".) I suppose one layer of indirection (into a constant) doesn't hurt too much, although it certainly makes things a little trickier.

The bigger problem is when the code constructs metric and flag names programmatically:

    prefix = "framework.client.requests.http.{status%100}s"
    recordHistogram(prefix + ".latency", latency)
    recordCount(prefix + ".count", 1)

    flagName = appName + "/loadshed-percent"

    # etc...

That kind of thing makes it very hard to find references to metrics or flags. Sometimes it's impossible, or close to impossible to remove, but it's worth trying hard.

Of course, this is just, like, my opinion, man!