HomeSync synchronizes our Macs' local accounts with their network counterparts. In other words, it's responsible for letting you work on your stuff at home and then upload it to the network when you arrive at school. The downside is, the more stuff you're HomeSyncing, the longer it takes to login/logout and the more strain it puts on the network. That's why everyone should customize their HomeSync preferences so only work-related folders are synchronized.
Finding the Settings
The HomeSync icon on your menu bar looks like a pair of houses. Click on it, then select Mobile Account Preferences...
This brings up a window showing which of your folders are being synchronized and how often. Most accounts are set to "synchronize everything in the Home folder at login, logout, and every 8 hours" by default.
Mine, as you can see, is set to only upload my Desktop & Documents folders. That's where I keep most of my important work files. I only have 3.4 GB (gigabytes) of stuff synchronized to the network, but I actually have 87 GB of stuff on my local account. The rest of it is either personal stuff (Music to get through the day: 7.6 GB) or so large I just back it up to an external hard drive (Copies of entire computers: 65 GB). If I ever tried to HomeSync all of it, the network would choke & die.
Many staff have similarly large accounts, most of it movies & pictures. A typical work document is ~30 KB (kilobytes) large. A typical high-resolution picture is 100x larger (4 MB, or megabytes). A minute-long movie? About 10,000x larger (400 MB). A 2-minute iMovie of your kid dancing can take up more space than 5 years of reports. While your work laptops have more than enough space for this (they typically have 100+ GB of storage), we get twitchy whenever a network account is larger than 6 GB.
Checking Your Space
Everyone should know how much space their stuff takes up, but the default Finder settings make it extremely hard to tell. Here's what I do when I want to see what's taking up all my space:
1. Click the Finder icon on your application dock (it looks like a stylized blue face) to enter the Finder.
2. Open the View menu and click on the very last item: Show View Options. This should bring up the window displayed on the right.
3. Check "Calculate all sizes".
4. Click "Use as Defaults"