Adisadvantage of using a sentence outline instead of a topic outline is that a sentence outline is often        

A disadvantage of using a sentence outline instead of a topic outline is that a sentence outline is often time-consuming to develop.

Explanation:

Sketching on topics is quick and time-saving and can address the entire subject quickly and accurately as it sets small reminders that let the reader know the full subject of the entire text.

However, a staged draft will also summarize the entire text, but in a very detailed and extensive manner. This is not bad, but it takes a lot of time and will make the reader use their time in an unoptimized way.