The application boxes are there to give CONTEXT for the brilliant achievements on your CV.
One of the biggest mistakes I see are resumes that use the bullet points to describe activities, tasks, duties of the job instead of pointing to specific contributions made that added VALUE to the company. Each job title should be followed by a short "job scope statement" but the focus should be on the bullets = accomplishments = showing how you do the job WELL. Exceptionally well.
On your MBA applications, the "description" section is where you can expand on the "job scope statement" or activities/responsibilities. The idea is that once the adcom better understands WHAT you do, they can better appreciate HOW you do the job well.
Also, in the words of David Simpson of London Business School, they are looking to see "the level you're working on." They want to know your role at the company, budget responsibility, how many direct reports, dotted line reports, mentorship responsibilities- what is this company counting on you to get done, exactly? You have already been VETTED by them and the school wants to lean on this information.
All this stuff is often missed on a CV, despite it being important information. Don't get sloppy with this part of the process, which is often left to the last moment. The school pays more attention to the application boxes than we do because 1) they created them and 2) it's standarized, comparable across candidates. It's important to have a clean, edited focused message for each application box. I personally call it a game of Twitter on steroids!
When it comes to length - quite honestly I like to look at the school with the tightest limits which is inevitably HBS ever @#$% time. They are MISERS (shaking fist.)
So to save time I will write for the shortest word count to capture the essentials and add parts in red for schools that allow more words.
In your situation, if you are only applying to two schools with no limits on this section, include all the information that is needed and nothing more. Make sure to pretend there is a word limit so the language is tight and crisp and easy to digest. I want to say this in all caps and it pertains to all sections of the application: INCLUDING MORE INFORMATION WILL NOT INCREASE YOUR CHANCES. Employ the Golden Rule on this, how much would you want to read here? After having read a bazillion applications? Keep it relevant, focused, high-impact.
Hope this helps!