What is the significance of tech group?

[Titus Caesar Vespasianus]

ie Western, East African, etc

[tinisiyo]

units have different pips on same military tech

[Vladimiś]

http://www.eu4wiki.com/Land_units

[Hurtman]

Different tech groups have different unit types - which give pips (aka combat effectiveness). The near and far east start out the best. Then, the West starts to become the best. Africa and the Native Americans start worse, and only get even more bad as the game goes on.

[SNEED]

Before the Tech system was reworked they determined how much your tech cost modifier is as well as the unit types

Now it's only the unit type AFAIK, which like already said, has the best ones in the eastern groups at the start but in the mid and late game western is absolutely superior