The bus/send method is very similar to what we used to do on the analog desks.
On the old Mackie 32-8's I used to patch a reverb or delay in to the FX send and loop it through the stereo returns.
This would give a mono guitar track a "
stereo like signal". Perfect for ping pong delay or spectrum spreading.
To break it down in newbie terms:
What a send does essentially is it takes the wet signal (The FX) and mixes it with the Dry signal.
The send knob adjusts how much of the wet signal (FX) you are hearing.
Using a tracks FX bin is different in that the whole signal passes through the FX and is varied by the input control of the Reverb or Delay unit (VST) itself.
More often than not when using a send you want your Wet to be at 100% but I have found uses for lower percentages as sometimes 100 can be over bearing even when the send knob is at lower settings. This is because each plug ins dry/wet control is different and react different.