Optional function invocation parentheses

[Will Rubin]

I'm new to D. While poking around the site I stumbled across 
Uniform Function Call Syntax. This lead me here: 
http://www.reddit.com/r/programming/comments/vvpfy/uniform_function_call_syntax_in_d_gamedevnet/c58f8yy

I seem to remember reading that empty function invocation parens 
were now optional so I tried it and it worked fine. But the 
comments in the above thread indicate that there is something 
special about removing them and it shouldn't be done so casually.

Are the following two "results" equivalent or is there something 
special going on behind the scenes that makes result2 less 
desirable?

import std.stdio;
import std.algorithm;

void main() {
   auto result1 = [1, 2, 3, 4].filter!(a => a < 4)().reduce!((a, 
b) => a + b)();
   writeln("Result1: ", result1);

   auto result2 = [1, 2, 3, 4].filter!(a => a < 4).reduce!((a, b) 
=> a + b);
   writeln("Result2: ", result2);
}