What does IEC 61850 mean for Power Systems?

A lot. There are many different approaches to describe the benefits. You can start with the System Specification Description (SSD according to part IEC 61850-6, SCL) and go down to the signals and communication. Or you can describe it bottom-up. I like the bottom-up approach:

1. Take a signal (e.g. Voltage phase A in kV) coming trough a serial Modbus (Address 12122) by polling into an IEC 61850 Server device
2. Give it a NAME (MyMMXU1.PhV.phsA) based on a STANDARDIZED Structure (Logical Node MMXU), and
3. Use the protocol (MMS, ISO 9506) to just poll the current value with a MMS Read.

We may have 10 bays with each providing the voltage phase A: then we could model this as follows:
Bay1MMXU1.PhV.phsA
Bay2MMXU1.PhV.phsA
Bay3MMXU1.PhV.phsA
...
Bay10MMXU1.PhV.phsA

That's some basic benefit ... for a first “"brief introduction”.

In addition (there are many other features to look at), e.g.:

1. MMS allows to retrieve the Signal List (device model comprising all logical nodes ...) ...
2. The system configuration language (SCL) allows to carry the "signal list" in form of an XML file ...
3. SCL could carry the complete signal flow between any device in a system: who has which signal to offer, who needs which signal, how are signals carried between the many devices (real-time, non-realtime ...) ...
4. SCL could carry the single line diagram (topology) of an electrical system ...
5. SCL could carry how the information is related to the single line diagram ...
6. …

So, does IEC 61850 add to the complexity of power systems? No that much! See also:

http://blog.iec61850.com/2014/10/does-iec-61850-add-complexity-for.html

Be aware: There is more than IEC 61850 that has to be learned, understood and managed!