Advantages & disadvantages
The greatest advantage of square threads is that they have a much higher intrinsic efficiency than acme threads. Due to the lack of a thread angle there is no radial pressure, or bursting pressure, on the nut. This also increases the nut life.[1]
The greatest disadvantage is the difficulty in machining such a thread. The single-point cutting tools or taps and dies used to cut the thread cannot have efficient rake and relief angles (because of the square form), which 
makes the cutting slow and difficult. Square threads also cannot carry as much load as a trapezoidal thread, because the root of the square thread is smaller. Also, there is no way to compensate for wear on the nut, so it must be replaced when worn out.[1]
makes the cutting slow and difficult. Square threads also cannot carry as much load as a trapezoidal thread, because the root of the square thread is smaller. Also, there is no way to compensate for wear on the nut, so it must be replaced when worn out.[1]
We're good on pictures here, but a little short on clear and concise explanation.