A Holy Paladin has a raid tier set from the Blackrock Foundry. If she switches to her Retribution spec, the tier set is still functional, as the primary stats and set bonuses change. However, if she prefers Haste for her Retribution spec and Crit in her Holy spec (and is someone who enjoys the min-max game), then a single set of armor may not be optimal.
For her healing set, let’s assume this player also has one ring with Spirit, a shield with Spirit, and a trinket that procs on heals. The trinket is almost useless in her Retribution set. The shield is also useless, since Retribution is designed to wield a two-handed weapon. The ring will be sub-optimal because Spirit is useless to a Retribution Paladin, but if it has another valuable stat (e.g. Haste), it may still be worth using—again depending on how min-max-focused the player is.
A more casual player would probably be fine just using the trinket anyway and using a lower Item Level two-handed mace when she plays Retribution. A more min-max player would probably want separate rings, cloaks, trinkets, neck pieces, and weapons to use in the different specs. A very min-max player—such as someone competing in world-first Mythic raid progression—might even want different heads, shoulders, chests, and so on depending on the mix of secondary stats. This player might even swap out gems between the two specs.
This may seem like a lot to take in now, but we’ll continue to watch feedback and answer any additional questions where we can. And again, keep in mind that as with anything still in development, this information or some of the details will likely change as we progress.
As always, we welcome your constructive feedback, and we look forward to reading what you think.