Series voltage source vs parallel voltage source

[WIlliam Powell]

Power systems isn't my area of specialty and I've been doing some reading where it was stated that series voltage connections are safer than parallel connection. I don't fully understand why though.
website address:
http://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/single-phase-power-systems/#

 

[Simon Bridge]

Welcome to PF;
Consider what is dangerous about the connections: what happens when something goes wrong.