Finding out what your customer's expectations are is always an important first step towards success. As a translator, you should check with your customer or project manager if updating the translations of exact or context match entries is requested, or not.
Simply put, exact matches are candidate, past translations found in the translation database (called translation memory) for a specific source language sentence. Computer-assisted translation (CAT) tools can help storing and retrieving source/target language sentence pairs. For example, CAT tools can store the translation for a sentence "Click Next to continue" and suggest the stored translation as an exact match next time the same sentence appears. CAT tool vendors even invented context matching features that remember near-by sentence relationships for more accuracy for translation suggestions. (I will separately discuss the types of matches in detail.)
So this sounds efficient, right? However, the question here is, is it really OK to use the exact match translation as it is, without making any changes?
The short answer is yes, in general. The exact or context match translation should normally be considered correct as long as the stored translations have previously been reviewed by the requester and the translation memory is in good shape. These reviewed translations already have the customer's preferred terminology, expressions, and necessary rephrasing according to various guidelines or requirements, such as language styles, company branding, and review feedback from the legal team.
Therefore, these high quality matches only need be checked briefly within the context of the new document being translated. If you, in your function of the translator, find any issue, do not change the translation. Instead, report your concern for the exact match translation using the communication features embedded in the CAT tools, such as comment panels and discussion tools. If you find too many issues in the exact match entries for a specific project, pause your task and check with the requester first to see if a) the existing translations have been reviewed in the past and b) corrections to existing translations are expected.
One of the exceptions would be very short sentences. For short sentences with one to three words (or four, depending on the source/target language combination), even exact or context matches need the translator's attention, because the shorter sentence can be more context-dependent. For example, a one-word translation memory entry such as "Watch" can have different translations for a system monitoring context and for a wristwatch in a product category.
In any case, it's best practice to always ask the requester if there are any concerns.