Do you always have to take the best (or any) save?

[Leez]

Not clear what you mean, Leez. Are you meaning to say the Preferred Enemy lets you choose to reroll your successes (to miss more often)?

In both cases a person wants to fail at one action to gain a later advantage. The Necrons's 2002 WBB is no more perverse then the BRB's 2008 Preferred Enemy. Your use of the word perverse is just baffling. Are we to also call tactics where one unit provides cover to another as perverse or people that use "bait" units as perverse?

A person wanting to purposely fail wound rolls or even not make them for the reasons Lerra posted, whether tactically sound or not is in the very same spirit that someone would not want to wipe out a unit they were assaulting in their own assault phase. For Preferred Enemy that is to prevent them being a valid target in their opponents next Shooting phase. The difference is, the Preferred Enemy rule is written very clearly as is the related Rage Embodied special rule for close combat, the former applies to "rolls to hit" the latter applies only to "failed rolls to hit". Whereas we're stuck with word "can" and phrase "has the advantage of" in the rules for saving throws, how does one justify reading "can" as "must"?

It's very natural for people to assume that everyone everywhere would always want to make and pass save throws and thus view this as GW's RaI, to read "can" as "must". It would be just as natural to think "who on earth would want to reroll successful to hit rolls" but here we are with tactically motivated reasons to deviate from the normal behaviour. We could plausibly take the wording in the saving throws section to be written with the word "can" to allow players this tactical option (probably Necron players with WBB would be the only ones wanting to do this). Is it not one of the standard GW memes that they do not write tighter rules because they do not want to restrict player creativity? This is however, in my opinion, faulty reasoning. In the end we only have RaW, and any RaI argument is little more then rulebook psychoanalyse.

In the end we have the word "can", so, what does the word "can" mean? Bluntly it means ability to-, permission to-, small metal cylinder with a closed end, not necessarily of worms, nowhere is "must do this or that" in it's definition.