"The Blue Minions' minds appear to be on a different plane of existence half the time. When they do decide to join us on this one, their healing and magical-damage skills can be most useful. They can resurrect fallen Minions during battle, but Blues are quite fragile, so position them carefully." - Minion Master Gnarl

As your loyal servant of darkness described they are basically your healer/combat-medics. So ask yourself why do you send them together with the horde expecting them to do damage against non magical creatures? It is this kind of reckless warfare which gives them their unjust reputation.

“A great tactician creates plans. A good tactician recognizes the soundness of a plan presented on him. A fair tactician must see the plan succeed before offering approval. Those with no tactical ability at all may never understand or accept it. Nor will such people understand or accept the tactician. To those without that ability, those who possess it are a mystery. And when a mind is too deficient in understanding, the resulting gap is often filled with resentment.” - Grand Admiral Mitth’raw’nuruodo (Thrawn)

And with this quote of an unrelated yet still blue skinned being we continue to our main goal of this lecture. How to get the most out of your Blues. Let's start with defensive tactics!

I'm sure you are aware of "Guard Markers". This makes the selected minions stand in formation without your guidance and makes you able to enact more complex battle plans. These are especially useful when setting up a defence and if you never use them because you are just charging into battle I implore you to reconsider (more upon this in the offensive section). Your Reds are the most obvious as holding a favorable position to rain there fireballs from is a good foundation. And your Greens can jump quite a distance upon the enemy's backs (which is crucial for winning the penultimate battle of the game against Kahn the Warrior). Browns just keep their position so I usually keep them in my personal unit. But the Blues should absolutely be put on a marker just behind them all. The reason for this is that once one of their cousins falls a single Blue will go to collect him. They don't bring them to you, but back to the Marker for resurection. Unlike the manual ordering this action cannot be misinterpreted as an attack order and lets the Blues focus 100% on keeping the horde alive and kicking.

Here is a simple defensive formation on even ground. If you want the enemy to come to you aggravate them with the Browns and retreat to let them walk in the trap. Greens can be moved further forward if the terrain offers a good ambush opportunity.

And now let's talk offence! Sometimes you will feel confident of your victory so you sent the entire horde. But your carelessness has gotten some killed and among them all of our blue minions. You just know that you can get a quick victory but a small loss now can have dire consequences (Especially on Legendary) for battels yet to come. This is why even in all out assaults it is wise to set up a field hospital.
Either set up the Blues in a favorable position or make them go just in front of you and charge the other minions in once you are happy with the positioning. There retrieve range is quite big, but if the enemy is spread out its useful to have them some wat near to the action.

"We live. We serve. We fight. We die. This is what we are, Sire, and what we will always be." - Blue Minion Mortis the "Resurrector"

And here we are! follow these basic tactical theories and build upon them. I hope that we will finally see some justice for all Blue Minions haphazardly sent to their demise and called useless afterwards. To all veterans and newcomers alike. Thank you for reading!