you could use mana barrier across a doorway or similar to block people entering with active spells or foci or etc.
make it harder for an opponent magician on the physical plane to cast spells at you.
Good points. But since the description of the spell starts with "Want a spirit-free room?", at least it is meant to be used for that purpose too.
Rituals are nice given the right circumstances. Specifically, when you have enough time and enough participants.
In case of Mana Barrier vs. Ward, note that the spell creates a barrier with rating (Magic + net hits), whereas the ritual creates a barrier with rating (net hits) only. Even with a lot of participants for the ritual, the teamwork test cannot provide more bonus dice to the leader than his original dice pool, so you'll probably never make a barrier as strong as the one you'd obtain with the spell.
You need 6 karma to make the ritual permanent. But you could also quicken the spell for a similar price (provided that you have Quickening of course).
To me the only saving grace of the ritual is the size of the barrier: up to 50 m³ times the sum of the participants’ Magic ratings.
Then you have the lodge of course, which, as far as I can tell, has no maximum rating. Provided you can pay for the materials of course. The only limiting factor is the availability of those materials I guess.