You may very well be correct
...and (s)he is.
the fact that your ip changes is the whole reason you need a dyn account in the first place ya?
Yes. The fact that your
public IP address is dynamic is generally the reason you would use a service like DnyDNS that will help you associate a domain name (constant) with a static IP address (potentially variable). For most home networks, this is referring to their only publicly addressable IP address, generally that of their router. Other devices that connect to that router generally have local-only IP addresses and are not accessible from the Internet. The router, by default, generally assigns these local IP addresses dynamically using a built-in DHCP server. You can assign your local IP addresses statically all you want with your router, but the one publicly addressable IP address you have won't care. A DynDNS hostname, for example, will refer only to your public IP address. That's all it
can refer to. The rest are specific to your home network and belong to a range of addresses that are not in use on the Internet because they are reserved specifically for private use.
(There are exceptions. You may have purchased a block of static IP addresses from your ISP and may be able to assign these to local devices. You would know if you did this. You did not.)
Sorry, but you are.
It is useful, but mostly within your home network. For example, if you want to add a printer to a computer based on a static IP rather than using Bonjour or something to find it for you, or if you have a device that you need to access all the time and an IP address works better than a hostname. It is also convenient if you do Port Forwarding (now we're talking external usage...) on Apple's routers, since they forward a specified publicly exposed port to a specified local IP address and port, and since you have to use an IP address rather than a host name to configure this, you'll probably want to make sure you have a static IP on that device.
But alone, it does very little for helping you access your home network from the outside world--and without a dynamic DNS service or knowledge of what your public IP address happens to be at that time, it does nothing at all.