Entries in group shadow file

[Al Sparks]

I'm setting up a server where one user is going to need access to
files on other users.

I'm in the process of setting group permissions and making entries in
the /etc/group file.

One thing I noticed when I used
   # vigr
is that if I made a change to /etc/group, it gave me the option of
editing the shadow group file.

I'm basically adding users to groups, where,
   somegroup:x:99:user1,user2

The shadow group file already does have users as members of various
groups starting out from a fresh build.

So my questions are, what is the downside of adding a user under a
group in the /etc/group file but not /etc/gshadow (the shadow file)?

Is there a way to automagically sync the
    somegroup:x:99:user1,user2
from /etc/group to /etc/gshadow?

I figure manually editing both files will increase the risk of
mistakes.
  === Al