I feel that people have altars for different reasons.
1. to create a field of merit, so that they are able to generate the merits by making offerings in this field of merit on a daily basis. very powerful and strong, when people clean their altars and do prayers within this field of merit
2. for them to stay connected with the supreme beings
3. for them to bless and plant seeds into the mindstream of others, their family members who are not pracitsing, as well as the animals that have the fortune to lay eyes on the altar.
4 For them to do their prayers to, so visualisation can be done through the help of the statues/thangkas/pictures on the altar. At least it helps one to focus, and people have a point of association with.
5. For people to create the aspiration to achieve the Buddha's body, speech and mind
6. It is said that when you are angry, one look at the Buddha's holy image can pacify your mind down. Since this is the case, the powerful ability for us to calm, pacify and plant seeds in our mindstreams, by having an altar close to us is extremely beneficial. Making an altar look beautiful cuts away our attachment to our senses.
7. But when people have altars, respect has to be shown irregardless of conditions and situations as this is your guide to liberation. The price to pay in you having an opportunity to get out of samsara is priceless.
I believe that having an altar does aid in one spiritual growth especially when prayers are being done as there is an object to make a connection and association with. Since I've had an altar, I have been much more motivated to be mindful of my surroundings as I have now created a field of merit, I am more motivated to do my prayers, and I now have a chance to gain merit by doing offerings. Of course, the motivation to your actions has to be pure in order for you that gain the merit.
Just a quick question though...is it necessary to have an altar? What is the consequences one faces if they do not have an altar?