they say that because the time capsule is designed as a backup device, 'regular' files are at risk of being overwritten if they are older than the backup files that are regularly overwritten to make space for newer backups
"they" are confusing Time Machine backups with regular data files. Two completely different things.
Time Machine has no idea how long a "regular" data file might have been stored on the drive...and it will always leave those files alone....even when space starts to get tight for Time Machine backups.
So, although I don't recommend it, as long as you have plenty of space on the drive, you will come to no harm if you know what you are doing and you want to store both Time Machine backups and regular files on the Time Capsule drive.
I'm guessing that "they" also did not tell you about the option to install one or more disk images on the Time Capsule drive....which will allow you to fully "reserve" or "isolate" a given amount of space for regular data files.
Disk Images were developed just for this type of purpose, but that might be another discussion. If "they" look puzzled when you ask them about using a disk image, then you need to look for more experienced folks.
Still, the fact remains that for most users, the best and simplest way to handle this is use the Time Capsule only for Time Machine backups....and use another separate drive for other data storage. That is what I recommend for most users.
Sharing the Time Capsule drive for both Time Machine and regular data files is fine....but best left to users who have a good idea of what they are doing.
On a separate note, I see that no one has trashed my LaCie recommendation yet. Stay tuned.
