Handedness assignment

I need an explanation for this Psychology question to help me study.

Which hand you use as your dominant hand is related to hemispheric dominance for language. Therefore, it is important to know hand preference in many psychology experiments. Several questionnaires have been developed to assess handedness, one of which is Oldfield’s Edinburgh Handedness Inventory. You can complete this questionnaire, provided online at http://www.brainmapping.org/shared/Edinburgh.php (Links to an external site.).

The test is scored by awarding one point for each “Right” response and separately awarding one point for each “Left” response. Subtract the “Left” score from the “Right” score and divide that difference by the total number of all responses, “Left”, “Either” and “Right”. Multiple that by 100 to get the Laterality Index. Generally, a score of +40 or greater is considered a right-handed individual and a score of −40 or less is considered a left-handed individual.

Please discuss the questions in the survey and talk about your thought about whether these are an accurate and thorough way to assess handedness or if there are better ways to perform this assessment. Also, how critical is it to know handedness?