You can store as much data as you want in a site  Collection. The problem is in
backing it up. You need to consider your recovery strategy. All content for a
Site collection  resides in a single database and the thought of having to back
up that much data at once... It is recommended that you try to keep your
databases to under 120gb in size

There are two practical size  limits on site  collection storage. The first is
the physical limit  on the size of a SQL database. That's over 524,000
Terabytes. I suspect you will run out of disk space long before you hit that
limit. But the second limitation is more critical. that is the size of a
database that your backup and restore system can handle in a reasonable time
limit. Having a 2 Terabyte SQL database will do you no good if you can 't
backup and restore it in a reasonable length of time. So the actual storage
limit for a site collection  is dependent on your backup and recovery system not
SQL or SharePoint. Most companies with standard equipment suggest keeping an
individual content database to about 50-100 GB.

Well said, and I would add that you'll most likely have locking/blocking issues
the larger your site  collections get. Large transactions can perform a table
lock and cause (temporararily), subsequent requests to be blocked. This is a
primary issue when dealing with large site collections. Either a few users and
really large site collections, or lots of users and small site collections. What
you want to avoid is really large site collections with lots of users. This
almost guarantees you'll have locking/blocking at the SQL level.

Your limitation will be at the content database. Not so much a limitation, but
a best practice based on your organization's SLA. Microsoft recommends that you
keep your content db's under 100 GB in order to be able to restore them in a
reasonable timeframe.