Every tracker you build in Analytics carries its own answer to one question: who else in your organization can see it. You set that on the "Who can see it?" step when you create a tracker, and you can change it at any time afterwards. KPIs, dashboards and home page cards all follow the tracker, so this one setting is what controls the whole chain.
This article explains each option, who it lets in, and what it stops them doing.

It controls who can open the tracker and everything built on it. It does not change the numbers themselves.
Two separate things decide what another administrator ends up looking at:
So sharing a tracker widely is safe. It does not hand anyone rows they were never allowed to see.
Three, shown as cards on the "Who can see it?" step:
Three lists, and you can use any combination of them:
They add together rather than narrow each other. "The North site, plus the Program Leads role, plus one specific coordinator" is a single audience, not three separate trackers.
Naming a role or a person is a direct grant, so it beats site restrictions. An administrator you name by hand sees the tracker even if none of their sites are on it. That is the difference between the people lists and the sites list, and it is the reason to reach for them when someone needs a number that sits outside their usual patch.
You have to pick at least one site, role or person. Saving "Specific people" with nothing selected is not allowed, because an empty audience would store as visible to everyone, which is the opposite of what you asked for.
Only the administrators and sites you already have access to.
If your own access is limited to certain sites, the people list shows administrators who share one of those sites with you, plus yourself. Administrators at sites you do not work on are not listed, and you cannot share with them.
If your admin role does not let you browse the admin list at all, the people picker is replaced by a single option called "People on my admin role". Ticking it shares with your own team without ever showing you who is on it. It is a complete option, not a degraded one.
An administrator who has been added but has not accepted their invite yet still appears, marked as invite pending. You can share with them, and the tracker is simply waiting for them when they sign in.
You decide, under "What can they do with it?":
This setting covers everyone the share reaches, whether they got in through a site, a role, or their own name. You cannot give one person edit and another view on the same tracker. If you need that split, build a second tracker.
Two people always have full edit rights regardless: you, as the creator, and account holders.
Yes. Account holders and administrators whose access is not restricted to particular sites see every tracker in the organization, apart from ones set to "Only me".

No. KPIs inherit their tracker.
If someone can see the tracker, they can see every KPI built on it. If they cannot, none of its KPIs resolve for them anywhere, including on a shared dashboard, on a home page card, and in an export. The same applies to edit rights: someone with "View only" on a tracker cannot edit its KPIs either.
This is why the tracker is the only place you set this. There is no separate sharing screen for a KPI.
A dashboard is an ordered set of KPI cards, and each card still answers to its own tracker. A card whose tracker the reader cannot see does not render for them. They see the rest of the dashboard normally.
The same holds for the KPI cards you place on another administrator's home page from the Admin dashboards tab. Before anything is written, that screen previews exactly who is affected, and if a KPI relies on a tracker some of those administrators cannot see, it names them and offers to widen the tracker for you.
Not always, and that is deliberate.
Access and data are separate, as described in question 1. An administrator limited to one site opens a shared hours tracker and sees the hours for their site, not the organization total. The tracker, the KPI and the wording are identical. The figure is scoped to the reader.

It takes effect immediately, and nothing is deleted.
Someone who loses access stops seeing the tracker and its KPIs the next time they load Analytics. Cards they had already placed on their own home page stay where they are but stop displaying, so their layout is not quietly rearranged. If you share the tracker again later, those cards come back on their own.
Switching a tracker to "Only me" does the same thing for everyone except you.
Yes. The Trackers list shows a short label on every row: Global, Only me, or Shared with a count of how many sites, roles and people are named. Opening the tracker spells out the audience by name.
If the share includes someone you are not allowed to look up, they are counted rather than named, so the line stays accurate without revealing anyone.
That depends on their admin role, not on sharing. A role controls whether someone can open Analytics at all, and separately which actions they can take in it, such as creating or deleting trackers, KPIs, goals and dashboards. Actions left unticked are read only: they still see the numbers, they just cannot change them.
Sharing decides which trackers a person can reach. Their role decides what they are allowed to do once they are there. Both apply.
If something is not behaving the way this article describes, please submit a ticket, or email us at support@vomevolunteer.zohodesk.com.