I would suggest if you are using the EDD for both Time Machine and your data that you partiotion it.
Remember when configuring the sizes for the partitions that the partition for Time Machine should be at least 3 times the size of the disk being backed up.
The downside to this solution is that Time Machine will not be able to backup the data,
If you need backup coverage for this data I would suggest you get another EDD for you data instead of the partitioning.
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Of course. You can use the external drive to make Time Machine backups and to store other data. The only thing you have to do is to create two partitions on the external drive through Disk Utility > http://pondini.org/OSX/DU3.html
After doing this, you will have to use one partition for Time Machine, and another one to store your files. It's important to make Time Machine backups, as they allow you to restore the whole system if the hard drive fails. See > http://support.apple.com/kb/HT1427
Do not do that. Dedicate a disk drive for backups and no other use. Get a second drive or a flash drive to transport changed files back and forth. Or simply get a second external drive for your storage needs.
I stand opposed to Allan's and mende1's proposition of partitioning the backup drive. If that drive were to fail then you lose not only your backups, but your other files as well. Keeping them separated is the best strategy against catastrophic data loss.
Hypothetically, let's say I do partition the external hard drive and use it both as a Time Machine backup device as well as a plain storage device. If I were to do this, would I be able to delete files off of my Macbook Pro then to free up space--word documents, pictures, etc? Thanks again for your help.