I been thinking about it for the last three years and figure the way the budget is, redundancy is more important then back up. Raid 1+0 for my set up.
So my question is, do I really need an off site backup for my OD information and data?
I work at a school and figure fire will not happen and theft only happens to the out skirts classrooms. Nothing inside campus has been stolen and no fires anywhere.
Do you use seat belts in your car? Why? I've never had a serious accident.
Your logic is faulty. when you say "we've never had a fire" that may be true but EVERYONE who has had a fire said "we've never had a fire". It is very rare to have it happen twice. Also your statistical sample size is very small (just your one school) with such a small sample size works like "never" don't mean much because the error bars are so huge
You can have off-site backup for
less than the cost of RAID. Use the same number of disks but keep some of them off site.
If your data is importent then you need multiple redundant backups. A common method is to have one copy off site, one copy in a locked fire safe and one near the computer, maye that one is Time Machine.
Use RAID only if you can't buy a large enough disk drive (because to have more then 1TB o data) of if you need better performance than you can get with just one drive.
A very common reason for lost data is simply human error. Some one deletes something and does not notice. RAID can't halp you there you need to go into your backup rotation and find a weeks old copy of the file. If you are on a budget Time Machine is a better use of disk drives than RAID1 (mirror)