Because it only syncs when you connect to the computer it has some inherent problems.
Your stuff is out of sync most of the day. So if you do a lot of updating, you'll never know which device is right. If you sync and edit the data on more than one device, then that problem multiplies by the number of devices.
Because of the large delays you will often end up editing stuff in several places before the next sync. This will cause conflicts, which you will have to manually sort out.
If you also sync online through one of the devices you stand a good chance of creating loops, and seeing your contacts and events multiply every time you do a manual sync. It is easy to overlook the iTunes sync, since it is not a setting on your device. At least half the time people come here complaining about duplicate this or that, it's because they are syncing both in iTunes and online.
In short, the iTunes syncing method is the least efficient method of syncing data that is subject to change on both ends. It was originally put in place before there were any decent online syncing available, and remains as a fall back if you have no choice, for whatever reason.
When ever possible you should sync all computers and devices back to the same place for each account/calendar/contacts or whatever, and by preference it should be as immediate a sync as possible. It helps prevents loops, duplicates, and conflicts.
And I realize in the below attachment the first and second options are identical. My mistake. I should have added a forth circle.