Unsyncronized parellel loops:

This is what happens with two loops where there is no attempt at syncronization.

at time 1, the user pushes a pedal which immediately begins recording, until he/she hits the pedal again at time 2. The loop then immediately repeats, but since it is of an unusual length, it will not remain synced up to the other loop which was recorded earlier (see picture).

Ever get two loopers together with two seperate loops pedals that can't talk to each other ..... thats basically the situation here.

Fully Syncronized loops:

Here we have the situation when one loops pedal is told not to start or stop recording until the master loop throws a repeat. So, the user hits a pedal at time 1, but the looper does not begin recording until time 2. The looper then hits the pedal to stop recording, but the looper does not stop recording until time 4.

The loops are perfectly syncronized because the newly recorded loop is always the same length, or a multiple of the first (in this case, the newly recorded loop is twice the length of the first for example.

Latching:

Here is a situation where the user tells the pedal to begin recording, which it does immediately. When the user hits the pedal to stop, however, the pedal waits until the newly formed loop is exactly as long (or a multiple of) the master loop. This way, the new loop can start or stop at any time relative to the master, and will always be synced.

The advantage here is that later when you stop playback of the second loops, and then start it again, it will know to begin playing at a particular location during the masters playback (instead of just being able to begin exactly at the master repeat).