There is a definent benefit to having one dometic altar in addition to whatever shrines etc you may want to have floating around the house. It was something I was thinking of after having done my morning prayers at it and since it has been floating on my mind this morning I decided to write of it.
1. The domestic altar gives a concentrated point of worship. Rather than having to do everything at various shrines for a festival or trying to decide which shrine to move stuff onto for a particular ritual, the domestic altar is open space 24/7 for any kind of ritual you may want to do. As it is often clear (or at least in my case it is pretty clear with the exception of some statues but otherwise no extras) you can move whatever you need onto the altar for a specific ritual. For example say during the spring when I celebrate the return of Apollon, well rather than choosing a shrine to celebrate at, I can move a statue of Apollon and a statue of Dionysos (the latter which I hope to have by then) onto the domestic altar and decorate the altar in accordance to the festival.
2. It can give you a neutral space to honor deities that you don’t maintain shrines for. This is valuable for me particularly since I do feel it is important to honor all the Olympians but don’t have a relationship with all of them that would include shrines to each in my home. This includes other gods that I might wish to extend a prayer and offering to for a particular reason but don’t even have a statue of much less a shrine.
3. It often serves as the centre of the household in so much that this is where the primary worship takes place. At this point I can’t move mine into the livingroom since my father is living with me but I do recognize the domestic altar as the spiritual axis of my home regardless of where it is set up. And as I chose a table with a drawer it is also the place I keep ritual necessities. This includes incense so that if I wanted to give a small offering at a shrine, I would still need to detour to the altar in order to get what I need. I like the way this works out personally because it links the altar with all the shrines in the house more or less, and so these shrines act more of an extension of it.
4. The domestic altar is a workspace. Whereas a shrine may have colorful bits of this and that which represents your relationship with the gods, and may invariably be a little cluttered without room for much else, an altar gives you a clear workspace where you can set out whatever you need and be limited to that.
5. The domestic altar is invariably where everyone of the household may worship. Unlike a shrine whch may set up by a singular person for the object of their personal worship, the family altar is literally in use by all members of the household who would care to do so. This connects back to the clear space of the altar and the altar being the spiritual center of the household.
So that is my short list of benefits of having a singular domestic altar even if you have a million other shrines. In the end I feel that shrines and the household altar serve different purposes.