English technical content is often written by non-native English speakers, or those with little experience in writing. The result is usually the same: a lack of focus and punch.
I am a native English speaker and experienced writer, well versed in the eccentricities and colloquialisms of the English language, and can shape imperfect content, pitching it perfectly for the intended audience. If the message lacks clarity: I sharpen it.
Some companies ask their developers to write technical documentation, with mixed results. Generally a developer's time is best utilized writing code, not documentation. Hiring a dedicated editor allows developers to do what you hired them for.
Sometimes even good content needs checking for errors by an independent professional with an eye for grammatical errors. My proofing service irons out the smallest of imperfections in written content, ensuring documentation is perfect in time for the deadline.