How does request.context in Parse Cloud Code work?

Question

Back in Parse Server 3.0 update, there was an addition of request.context to pass data between BeforeSave and AfterSave as documented here:

https://docs.parseplatform.org/cloudcode/guide/#using-request-context

However, I'm having a bit of trouble understanding how and when Parse runs this code in the example.

const beforeSave = function beforeSave(request) {
  const { object: role } = request;
  // Get users that will be added to the users relation.
  const usersOp = role.op('users');
  if (usersOp && usersOp.relationsToAdd.length > 0) {
    // add the users being added to the request context
    request.context = { buyers: usersOp.relationsToAdd };
  }
};

const afterSave = function afterSave(request) {
  const { object: role, context } = request;
  if (context && context.buyers) {
    const purchasedItem = getItemFromRole(role);
    const promises = context.buyers.map(emailBuyer.bind(null, purchasedItem));
    item.increment('orderCount', context.buyers.length);
    promises.push(item.save(null, { useMasterKey: true }));
    Promise.all(promises).catch(request.log.error.bind(request.log));
  }
};

in other examples, cloud code functions are run via Parse.Cloud.beforeSave or Parse.Cloud.afterSave. In this example above, the function beforeSave is assigned to a

const beforeSave.

Why was this done and is this supposed to be placed inside main.js top level or inside another function?