Other than personal preference, are there known to be advantages or disadvantages to meditating in a group instead of alone?
Think about it - we go to refuge to the Buddha, Dharma, and the Sangha. If community wasn't important, it wouldn't be one of the Three Jewels. There's ample scriptural support for this as in Dhp 6.78, the concept of the kalyaṇa-mittata or spiritual friend, and the Upaddha Sutta where the Buddha called admirable companionship the "whole of the holy life". While it can be difficult to find a group where you feel "at home", being around like minded individuals striving to the same end will only bolster your practice. Furthermore, even those tiny annoyances like someone shifting during meditation, someone coughing, or a loud breather help strengthen your concentration and resolve. Life is not perfectly collected samadhi! We need to learn how to overcome obstacles. What better time than when you're on the cushion! I think it important to add that monasteries are supposed to be places most conducive to the spiritual life. If solo meditation was somehow "better" than group meditation, then monks would not sit with each other. Needless to say, this is clearly not the case.
I will also say that personally, I always sit more deeply when I meditate with others. The ritual of driving to the same place, seeing the same people, and feeling the energy in the room - nothing can replace that!
As off color as this metaphor is, I feel the need to share it. One of my teachers once told me that meditation without community is like sex by yourself - it's pleasant and effective, sometimes something dramatic occurs, but always there is the sense that something is missing! :-)
In my experience, group meditation gives one encouragement and adds a new dimension to one's practice. The sense of community is also helpful.
A disadvantage of group meditation is that groups vary in their qualities and it might take a while to find the right group. I've tried 3 in my city, and only one have I been able to take seriously. They consider themselves Buddhist, and they apply it to their lives in an honest and genuine fashion. The meditation session is uncomplicated, consisting of beginning and ending chanting, a 50-minute sit with a break, and a short reading passage from some Buddhist literature. This group is affiliated with one of Ajahn Chah's monks.
Of the other two, one was in it for the money, and didn't give me a feeling of community. The last one is sort of a secular mixed bag of traditions that doesn't seem to settle on any one practice.
I have a slight preference to meditating alone, but I try to make it to my group's weekly meet when I can, as it provides me some consistency that I wouldn't otherwise have.
Even if very usual and very popular, could anybody remember a group meditation in the Tipitaka?
Its good to learn together, improve each other, talk on Dhamma, but behind of that, if it is a matter of real battle and seclusiveness, there is really no reason for "coupling". Brahmacariya has many levels.
The only benefit it has is that the governing principle "Cosmos" is very present, since most do not so much believe in "supernatural" things. Atma is sure that most of you know the supporting thought: "If I give up now, they will think that I am a bad meditator".
So for simply such purposes, or to have a teacher aside, to watch and assists, such as gathering together to make basic training is good. As for doing the real "job" it really has no value but simply a lot of distraction potential. Yet it sells and bind many costumer to the provider. One needs to think about if his/her aim is to get independent or even more depended. Just think on the many trouble in and around of groups.
Nekos comment that there is a kalyanamitta required , when it comes up to your own work, is quite miss-understood. A gathering in certain groups simply provides with outside necessaries.
Upasakas Suminda Sirinath S. Dharmasena argument in regard of "conditioning / fabrications in the environment" could be only valid in regard of giving a good sample or such as visible assenting, which people at large would naturally follow. But that's all. The rest might grow in the area of the mystics of "Buddha-field", but such is more a Tantric and worldly thing.
Even thought of disturbance of beings in other spheres, remember the metta Sutta. So a mass of people entering an area, are naturally not able to do not disturb at the first place, even if they are later more separate.
To do such things like occupying even public places with such things, what does is it actually directed to, aside of occupying?
Training and learning good, just as a start or sometimes improvement. For actually working, no. No need at all and no where suggested by the Buddha, as far as Atma is aware of it. It simply sells, but not awakening at least.
When meditating, this creates conditioning / fabrications in the environment around the meditator. So when meditating in a group such conditioning can effect each and everyone in the group making your meditation more productive.
Similarly for any good action if you do as a group the results / karma is stronger than doing solo.