Why is "do + VERB" not a great construct?

When you think about writing do + VERB, you're using a weak construct.

• She does swim like a seal.
• I do think you're the best person for the job.

This construct takes the drive out of the sentence and often sounds old-fashioned.

Instead, simply use the verb:

• She swims like a seal.
• I think you're the best person for the job.

In these examples, the meaning is clear, and the picture forms more quickly in the reader's mind.