So, here's a fun story:
We have a student who graduated last year. That student, while they were a student here, used their school credentials to create a bunch of personal accounts.
Then, they graduated. Now, they live in Grand Rapids. Mr. Brackett knows what street and what house they live in. He knows the balance in their bank account. He knows what they ordered for take-out last week. He knows where they applied for a job last month.
Or, how about this story:
There is a freshman who is using their school account to create online banking accounts for themselves, including accounts on Venmo and PayPal. So, now Mr. Brackett gets notifications every time that student buys something or sells something with one of those accounts.
When you use your school account to sign up for personal services (apps, websites, etc.), you are giving access to that information to the school and its Technology Department (that's Mr. Brackett and everyone he works with).
Maybe, these situations don't seem that bad to you, but consider this:
Imagine if Mr. Brackett ever has to share that information with anyone who asks for it.
For example, if the police, or lawyers working with the police, ask Mr. Brackett to provide information about what a student is doing with their school accounts, Mr. Brackett must obey that request. If the police ask about the student who graduated last year, and if they ask if the school district knows anything about their current location, Mr. Brackett has to tell them what he knows -- everything. Or, if the police ask about the banking activity of a certain freshman, Mr. Brackett has to tell them what he knows -- everything.
Creating a personal email account for yourself is fast and easy and free. AND IT'S A MUCH BETTER CHOICE THAN USING A SCHOOL EMAIL ACCOUNT.