I think it is too easy to slip into the habit of using shrine and altar almost interchangably, after all we pray at both. Even I have caught myself saying altar a time or two when discussing my shrine for Apollon, but in reality they are very separate and have their own functions in the household.
An altar is where the general worship of the household is conducted, where the kharis between the oikos and the gods is predominantly carried out. As such it tends to be rather formal looking, clean and simple in design. It is more less the “work area” of the household. Adornments, if done, tend to be seasonal or for specific festivals.
I have two altars in my home (although I am planning ancestor altar). At the door I have the rudimental beginnings of my doorway altar where the gods who protect the entrance are honored. The crystal representing Apollon Aygieus is temporary until I find a suitable black stone. I have also yet to find a good stone for the herm, and it lacks images of Artemis Prothyria, Hekate, Herakles and Zeus. This altar in any case perserved the oikos by the woship there.
The second altar is at the center of the house where Zeus who ruled the center of the house is honored along with all the gods of the oikos. As I do not have a house with roof access as was anciently had and I have had the pleasure of experiencing in Morocco, I cannot set up an altar on the roof for the Dioscouri. So they too are worshiped at this central altar. I am slowly working on providing images of all the household gods on it. This altar is the heart of the oikos.
Shrines, on the other hand are usually set up for selective gods where personal worship is offered. The shrine is for our relationship with the gods so honored there, and are typically created because the god or goddess is highly favored. Shrines continuously change and evolve as devotional items are added. Most of my own are still rather sparse. Shrines tend to grow organically in my experience, so no two shrines will grow at the same rate.