[icedchai]

You don't need private addresses. You may need non-routable addresses, but they do not need to come from a "private" network range.

[otabdeveloper4]

A distinction without a difference. Private addresses are those that aren't globally routable by definition.

[amluto]

Your definition is questionable. There are:

(a) addresses that are globally unique but not globally routable. (These are extremely common in IPv6. These are not so common in IPv4 because IPv4 addresses are expensive, so people try to minimize usage, so people will try to avoid using paid-for globally unique addresses for non-routable purposes.)

(b) addresses that are in ranges that are, per spec and actual usage, only even defined within an organization and are not globally unique. For example, 192.168.0.1.

(a) and (b) are not the same by any useful definition. Sorry.

[icedchai]

The difference becomes apparent when you connect or combine organizations using the same private range. It's a lot simpler to route networks (not globally, privately) when the ranges are unique. There's no NATs, double NATs, and other nonsense to deal with.

Even without this, it's a lot simpler administratively. I have about 20 AWS accounts, all with their own VPCs, all using the same 10.0.0.0 block because... well.. nobody thought about this. What do I do if they need to communicate? (They probably won't, but...)