They facilitate storing and retrieving of industry-specific terminology. The human translator is working interactively with the software to finalize the translation. Post-translation editing is almost not necessary. The level of benefit will increase with the amount of repetition in a document. Long technical manuals and previously translated documents are good projects for these tools.
Products are expensive and designed for the professional translator.
MT systems are only available for a limited number of languages, mostly European languages like English, Spanish, French, since the rules for analyzing text vary by language, and are mostly priced and sold by the specific language pair. Such translation engines include extensive dictionaries that must be maintained by a human translator. Use of jargon or terminology that is not defined in the dictionary can falsify the translation. Complex and abstract sentence structures can also impact the quality of the translated document. MT programs are still not able to capture accurately all the meanings and nuances of written language.