User blog comment:KachiExa/Servant's Best Craft Essence Guide-1★ & 2★/@comment-33940255-20180410053742/@comment-34352073-20180410094109

Despite not being the OP (or an expert), I can try and give some examples (1 for each class for now) as to Servant role and CEs, I guess:

Arash: traditionally, he's just a damage dealer, his point being to get his NP off at the right time and then die off. If you wish to find other uses for him, you could try to use him as a pretty bulky, steady damage dealer. Then when he's almost dead, you fire off his NP. This is especially useful for protracted battles, most prominently when you've got his Bond CE (and possibly the Chaldea Combat Uniform). A good CE for the first role is as mentioned before, and for the other, any Guts-giving CE to ensure he actually gets that NP of his off. or, maybe.

Benkei: To me at least, Benkei doesn't seem like someone you'd take for his NP, but rather his skills. His role would be that of a support (with 2 Q and 2 A cards, he can help get chains off), debuffer or tank (although he doesn't shine in this role with 1 turn of taunt per 5 turns). I feel the best way to augment his role is the aforementioned debuff success rate CE, like. His Bond CE, though bland, helps too. Maybe pair him off with Tamamo (Caster) and a dedicated damage dealer.

Blackbeard: He's... odd. His best use, as mentioned before, would be in an all-female team of Servants with damage-dealing NPs to get the most out of his 1st and 3rd Skills. As he can function fairly well as a healer, seems like the right CE.

Shakespeare: Like all the other bronze Casters, Shakespeare is a support Servant, built for Buster teams. Preferably ones with powerful NPs, especially ones that benefit from overcharge. Depending on your team composition,  can be useful for Berserker teams, and maybe or  for less squishy teams.

Sanson: He's a bit problematic. By his skillset, he seems to be built as a sustained damage dealer, but he doesn't seem to have the chops for it. I feel he fits best to taking care of regular Human-attribute mobs. In a regular mission, he would probably be able to get his NP up by the time the 3rd wave is reached, and could then use it at his leisure. Perhaps he might benefit most from CEs that flat-out increase his damage, such as, and  to name a few.

Caligula: Regular damage dealer, relying on Busters. On no account, though, should you try and rely on crits with him (his Star absorb being one of the lowest in the game). As mentioned above, Buster-up CEs are good for him, but I've also found that works really well, giving him a heal of 1750-5250 every 7-5 turns. His NP, if you get him to use it, is also hilarious in boss battles, especially against Archers and Assassins (bring overcharge).

Something along those lines, anyway.