Difference between conditional expression outside/inside the aggregation function?

[#1]

What is the difference between

1. A conditional expression outside the aggregation function, e.g. If( <Condition>, Sum( <Expression> ) )
2. A conditional expression inside the aggregation function, e.g. Sum( If( <Condition>, <Expression> ) )...

I got an article regarding this

Qlik Design Blog : Conditional Aggregations | Qlik Community

but still couldn't be able to clear my confusion.. Please let me know about this..