Alright after the last tournament I attended last weekend I thought it would be a good idea to share some of my thoughts on decoy units. I used a 8-man terminator squad and the emperors champion as the decoys of my rhino rush army. To act as a base I'm using one of the games I played at the tournament, but I've simplified it (I just want to make my point).
The game was base objectives with spearhead deployment. That is pretty much the perfect mission to bring rhino squads from reserve. The fact that you can bring units on from your entire table edge, means that your almost outflanking.
At the tournament you got more points for holding your opponents objective, so it made keeping units in reserve like even more sweeter.
Now here comes the important part. I could have elected to just reserve everything, but I believe that opponents than tend to deploy his or her forces to defend attacks from the entire board edge, So I depolyed my decoy unit of termies and my 3-man bike squad (all armed with meltaguns) to give my opponent an impression of where his or her enemies are.. Sorry this picture is missing the objectives.
I charged forward my termies, blasting the penitent engine, a chimera and most of it's occupants, being as intimidating as possible. My opponent had left one chimera in reserve. To make sure he wouldnt outflank me, I turbo boosted my bike into the far corner. He took the bait and drove up beside the bikes, deciding to try and flame them. The bikes and chimera would play cat and mouse up until turn 5. The guardsmen inside would have lost their chimera and only moved up 6" from the table edge. Yes the bikes are dead, but those guardsmen wouldnt be reaching any of the objectives in the last 2 turns.
When my reserves arrived, I deepstruck the dreadnought to take out the chimera which was going around the termies. The multimelta exploded the tank, and the sisters proceded to charge it (the superior had an eviscerator and there was a priest with an eviscerator). Since I would get more points for my opponents objective I brought 4 tanks up the right edge, and only one onto my own objective.
By the time my opponent ate through the distraction termies, bikes and dreads, he wuld be very out of place, and my templars would have overwhelmed the one guardsmen squad that was defending his own objective. He did deepstrike a unit of seraphim with a canoness next to my objective, blowing up the rhino and killing the guys, but due to the funny scoring system I still got 18 points out of the maximum 20.
This post is long and you may not agree with my points, but I've shared my thoughts.