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Pro Smart updates to big files
If a small portion of the file is changed it sends/receives only the differences (not the whole file), which is fast and bandwidth-efficient.
Pro Easy to use
You can use Dropbox via website, by installing a desktop client that creates a folder that you simply drag and drop files into, or with their mobile app. Everything synchronizes across all devices used and cloud storage. And Dropbox offers easy methods of sharing whatever is within it.
Pro Allows sharing a single file via link
Whether using desktop client or web interface, simply right click on the file you want to share and select Dropbox > Share link, then send the link to the people you want to share the file with. The recipient does not require a Dropbox account.
Pro Allows sharing a folder
Using a desktop client: right click on the folder you want to share and select Dropbox > Share This Folder, then enter the e-mail addressees of people you want to share the folder with.
Pro Cross-platform desktop and mobile
Dropbox is available on iOS, Android, BlackBerry, Windows, OS X and Linux. By having a client for so many OS's pretty much anyone is covered no matter what kind of device or OS they are using.
Pro 30-day version control
Dropbox keeps deleted and earlier versions of files for a month.
Pro Desktop client has no file size limit
As long as you have enough storage available, you can upload files of any size using Dropbox desktop client.
Pro Up to 18GB of free storage space
Dropbox personal accounts start out free, with 2GB of space, but users can get extra space by recommending the site to friends, or taking part in events like "Dropquest", where users can win extra space by solving puzzles.
Pro Instant disaster recovery
Your files always synced online means instant disaster recovery. When your hard drive becomes unbootable, pick up another laptop and just carry on with your life from where you last saved.
Pro Lots of addons and integrations
There are official and third-party Dropbox add-ons that extend the functionality of the service and add ease of use of existing features.
Additionally, Dropbox can be integrated with existing applications to bring its functionality to other apps.
Pro Folders can be downloaded compressed to save bandwidth
To save bandwidth and download speed you can choose to compress a folder into a zip archive for download.
Pro Available free storage can be increased with referrals
You get extra free space for you and your friend if they sign up.
Pro Adjustable bandwidth use
To not slow down the network or save traffic you can limit the upload and download speeds of Dropbox.
Con All-or-nothing (non-selective) upload
Uploading generated contents (cache, compiled code, etc.) is prone to conflicts, wastes bandwidth and free space.
Con Not secure
They don't apply end-to-end encryption, files are visible to admins, governments, etc..
Con Too little free space
There is just too little of free space available comparing to the competition.
Con Does little more than storing files
Con Problems when synching between Linux and Windows devices (unconfirmed)
This summer I lost thousands of files due to this problem on older projects which subsequently needed revising and had to be rebuilt as tons of the source was gone.