There's a lot of misinformation around mic boosters, so I did a quick test to see how much of a difference boosters ACTUALLY make.
Turns out, while it helped reduce the noise floor a bit, the difference was a lot smaller than expected. Even reasonably affordable preamps are pretty good these days. The biggest advantage I found was the convenience - an inline mic booster could mean less manual boosting after the fact in your DAW or other applications, use on the go with a camera preamp, or less noise with a mic in a live setting with unknown preamp quality.
In a controlled setting with a decent quality preamp and close mic distance, a booster is a nice luxury and can reduce the noise just a bit further, but isn't the absolute necessity that some proclaim it to be.
(Headphones recommended of course! Here's hoping KZread's compression doesn't affect the "silent" parts of the tests.)