[GNC] Why does the sample "investments" account tree have intermediate "Bond", "Mutual Fund", and "Stock" accounts?

[Jim DeLaHunt]

Hello, folks:

I have been using GnuCash for a long time, starting with the GnuCash 
template account tree and modifying it gradually, but never thinking 
hard about it. Until now. I am adding a bunch of investment accounts. 
This makes me look more closely at the template account structure 
depicted in 
<https://www.gnucash.org/docs/v4/C/gnucash-guide/invest-setup1.html>.

This structure is:

  * Assets
      o Investments
          + Brokerage account
              # Bond
              # Mutual Fund
              # Stock
                  * AMZN

What is the reason for the template inserting the layer of subaccounts 
between "Brokerage account" and "AMZN" (for Amazon.com stock)? Why 
shouldn't the child accounts denominated in each security be directly 
under the "Brokerage account" account (as long as the parent account is 
denominated in the currency which the securities are priced in)?

For my own purposes, it seems simpler to me to have the per-security 
child accounts be directly under the "Brokerage account". Is there a 
rationale for the intermediate accounts which I am missing?

Also, in the template, the "Brokerage account" is of type "Bank", and is 
not a placeholder. That seems to imply that cash and cash-equivalent 
transactions should be applied directly to "Brokerage account". Somehow 
I ended up making a child account "Cash CAD" (or "Cash USD", or 
whichever), and applying all the cash-equivalent transactiosn there. My 
equivalent of "Brokerage account" has no transactions, and is often a 
placeholder account, and has account type "Asset" rather than "Bank".   
Is there a reason to put the cash transactions directly in the brokerage 
account, or is this a matter of personal preference? (In which case, I 
will keep the structure I have.)

Thank you in advance for your insight,
      —Jim DeLaHunt