One of the particularities that i ran into while start using Siemens Step7 is programming based in Symbols, it is very critical understanding the difference between programming symbol based or address based since they are both powerful and knowing how to use them can help you save hours on projects, especially if you have a whole system with standard programs and you need to do constant upgrades to the complete system, but also in some other occasion when you need to do drastic changes on an existing block or group of blocks.