While based in the same language, the two communication forms have different conventions. Spoken English tends to be more fluid and accepting of deviation, often because voice carries additional identifiers of meaning, such as intonation, for example. Written English, on the other hand, has simply the visual image of characters collected together, thus leading to more rigidity in its conventions.
Consider the suffix -wise for instance. Spoken English often accepts this suffix at the end of words to communicate a relationship with a given aspect — the noun to which the suffix is attached. Thus, we have words like lengthwise, a word which conveys a relationship with length. Words such as lengthwise have a long history of use and acceptance. Many other words with the -wise suffix do not. Although the conventions of spoken English may tolerate that, the conventions of written English do not. More effective technical writing requires more formality.
The example sentence in the cropped graphic above provides a good demonstration. It is perfectly acceptable in spoken English, but in written English it does not convey the formality that often attends more effective technical writing. The writer can correct that deficiency with a slight change to the end:
Be wise with -wise. The most effective technical writing is not simply transcribed speech. The most effective technical writing respects the difference between spoken English and written English to convey better the message intended for your audience. And that more effective presentation will represent you and your brands more effectively as well.