Guardsman Marbo

Ok, so this dude has WS 5 BS 5 I 5 has a sniper pistol, a democharge, and wounds on a 2+ in Close Combat. Oh and did I mention he can come in ANYWHERE. For a meager 60 points, you can field this silent killing machine. And he can wreck house anywhere and anytime. Toe to Toe with space marines, what a joke, Toe to Toe with tanks, what a joke. Used right, this guy is insane for his points. Used wrong, Your enemy gets a kill point, and all he had to do, was shoot him. Because at the end of the day, Marbo is S3 T3 with a 5+ save, and can't do anything out of CC worth mentioning, with his short range and relative lack of firepower.

Using him right relies on your overall scheme. If you want a durable unit, that is just gunna be a durable unit, bring him in somewhere, and go to ground, 2+ save. Put this guy next to an objective and do that, and he can aid greatly in pushing the enemy back. But more often than not, this little guy will see himself launching suicidal one man raids on enemy heavy support. Throwing his democharge into gunlines, or acting as a speed bump. As long as this guy gets to throw his demo charge, and get stuck in CC, he'll pretty much earn his points. If you can make him last two turns, then he will work for you. Three turns? your opponent obviously just has no idea what he's doing if your Marbo lasts three whole turns.

How to use him wrong: this is far more important than above, as well, that's common sense. Here we have a tad bit of Forethought. Basically, don't put him in CC against units that are too soft, unless he can easily consolidate into more cover. Don't EVER, leave him in the open without cover. Unless you are fine with him dying after one unit shoots at him, in which case go right ahead. Next up, don't put him in over his head. It's tempting to just throw him at some terminators, but don't. He'll lose that battle 9 times out of 10, easily. Don't throw a goddamn demo charge, if he is surrounded by friendly units. JUST DON'T DO IT!

lastly, why not to take him: kill points, and fighting armies built for CC are fine reasons to leave this guy in the same shadows you found him.