One of the main issues Games Workshop designers have is the lack of scalability in their points system. With "Spam" being an often used and often loathed tactic in the game each codex author is forced to treat each entry as if it will be maxed out. Thus many Elite choices are still-born ideas - scuttled before they can even be considered for inclusion. Because there is a real chance that their above-average abilities will become game breaking when used en masse every model is costed to reflect this danger. Hence 16 points per model for a Storm Trooper, 40 points for an Ogryn and, God help us, 30 points for a Damned Legionnaire.
The Legion of the Damned entry is a ghastly miscalculation. A poor, poor joke on anyone that was excited by skeletal marine models and hot-rod flame designs (admittedly a niche within a niche). A unit of five starts at 155 points and will shoot up to 215 with the obligatory multi-melta, melta, combi-melta combo (to make the most of their obligatory derp strike).
So you have a 200+ point unit with no deployment options and no real role on the battlefield beyond stoic meltacide. What stands between this overpriced gimmicky unit and oblivion? The Unyielding Spectres special rule was cause for much "oooohing" and "aaaaahing" many moons ago when the codex was still fresh and a 3+ Invulnerable save was the feline's sleeping garments. To the more astute observer, however, a 3++ isn't worth much when attached to a 3+ model. What this means, essentially, is that despite all their bells and whistles this Terminator-costed unit will die to approximately 15 wounds or 3 wounds per model.
Meanwhile the Legionnaires suffer horribly from a lack of mobility. Slow and Purposeful means Relentless as well needing to roll as if in difficult terrain when moving. Units with this rule generally benefit from being in cover as often as possible (where only the benefits of the rule would be in effect) but seeing as the rules for cover are stupid being obscured does nothing for the unit's survivability. Moreover although S&P is a hard drawback in and of itself for a unit with no transport options the unit's weapons are also costed at a ridiculous premium.
So lets get this straight: You have to buy a set of ridiculously mis-costed models and then pay again through the Slow and Purposeful restriction. After that you can pay a third time since only a couple of models in the squad are useful beyond soaking up wounds allowing you to top it all off by giving up a total of 50 points for two melta weapons (whose ability to hit is not augmented in any way setting you up for the ultimate Failpocalypse when both shots whif).
Well at least you get 2 Attacks base! And the Damned Sergeant has WS 5!
Luckily someone did take a glance at a scatter die and notice that this unit will scatter 2 out of 3 times. So they gave us a re-roll which might help. It's not terribly likely to be an accurate Deep Strike even so but every little bit helps I suppose.