Translation memory can certainly improve productivity. Many purchasers of translation are of course aware of this, and want some of these productivity benefits passed on to them. This usually takes the form of offering discounts for sentences/segments already in the translation memory, and sometimes for fuzzy matches.
But this can be taken too far. Some clients will ask not to pay for 100% matches or repetitions at all.
On the face of it, it sounds reasonable — it’s already in the translation memory, so why should they pay for it twice? But there are two problems with this. First, it assumes that inserting the 100% matches/repetitions into the translation involves no work by the translator. This isn’t true; even 100% matches need to be checked for context in each situation.
To give a very simple example, Japanese doesn’t have a capital/lower case distinction. So if the same Japanese sentence is used in a title and the body of a section, you need two different English translations for it. One will be in Title Caps and follow English conventions for titles (e.g. leaving out articles), and one will be in sentence caps and follow normal English grammar conventions.
Also, Japanese very frequently elides the subject and/or object of the sentence, and verbs lack conjugation for person and number. On this basis alone, the same sentence can have many different translations depending on the context. He/she/it/they/we [will] put/puts it/them/him/her/us/the widgets on the list/in the box/over there…
The other problem stems from this dependence on context. Because context is so important to a translation, especially between languages like Japanese and English that are very different syntactically, you’ve got to pay a lot of attention to those 100% matches just to keep up with the context. Furthermore, if you’re using a translation memory created by someone else you have to pay even more attention in order to conform your translation style to the memory; otherwise, you’re liable to end up with some unreadable Frankensteinian hodgepodge of different styles and terminology.
It also follows from the above that simply leaving out the 100% matches, and sending you only the “new” parts, is even worse. You’re then left with a disjointed list of sentences and no idea of how the sentences fit together.
So sure, offer a discount for 100% matches. But think very carefully before offering to insert those 10,000 words of perfect matches for no charge.