Tactically why would a Eldrtich Knight what a familiar?

[CyberThread]

His using one of his slots to learn this spell. Is it just a character flair choice, or some sort of metagaming optimization going on that I may not know of?

[Knaight]

Familiars have their uses, but there's no reason to think that there's any metagaming involved.

[Jeebs]

You can make the Familiar take the Help Action to give allies Advantage on one attack. Pretty great for Rogue allies and Sneak Attack.

Or you can have the Familiar cast Shocking Grasp and other Touch Spells.

When the bad guys get sick of the Familiar they have to use an attack to squash it. Especially if it's an Owl with Flyby Attack -- they can't just whack it with an Opportunity Attack. That's one attack that isn't targeting the rest of the party, even if it does mean spending the resources to resummon your Familiar.

[CantigThimble]

An animal spy and/or deliverer of touch spells can be handy to have around. The only cheesy thing that could be done with it is having it assist you on everything always. However if you just rule that it can't assist on things it is incapable of doing on its own then that's not an issue. (Attacking, arcana checks, ect.)

[Felvion]

Additionally to what has already been mentioned it also saves him slots. He cast it once, gets all the benefits a familiar gives and doesn't have to cast it again until the familiar dies or he really wants another form. He could actually even swap the spell to increase his spell selection and make sure his familiar doesn't die but this would be a very risky decision.

[bid]

The help action is a strong point of contention as RAW can go both ways. I would not consider it unless your DM approves it.

[Slipperychicken]

Familiars are nice to have overall. They can make scouting easier, along with other benefits like carrying messages and grabbing really small items.

[E’Tallitnics]

The help action is a strong point of contention as RAW can go both ways. I would not consider it unless your DM approves it.

Last week JC again reiterated that a familiar can use the Help action to aid an ally in an attack: http://www.sageadvice.eu/2015/12/09/familiar-help/.

[bid]

Last week JC again reiterated that a familiar can use the Help action to aid an ally in an attack: http://www.sageadvice.eu/2015/12/09/familiar-help/.
Nice to have it clarified, thanks.

[Tanarii]

Last week JC again reiterated that a familiar can use the Help action to aid an ally in an attack: http://www.sageadvice.eu/2015/12/09/familiar-help/.
I was going to say that's a terrible ruling, but he's absolutely right. The 'attempt alone' phrasing is from the ability score (skill) checks section. The Combat Help action doesn't say anything about it. Which means it only applies to ability score checks.

[Dalebert]

Last week JC again reiterated that a familiar can use the Help action to aid an ally in an attack: http://www.sageadvice.eu/2015/12/09/familiar-help/.

I thought I'd heard this as well. Thanks for verifying. You can certainly house-rule against it but the proper thing would be to tell him about that rule before he spends a slot on it, or else allow him to switch it out.

I can't think of anything particularly devious or min-maxxy about it. As folks have said, they're just damn useful. It's nice for someone to have one. If there's another caster in the party who can do it better, e.g. a warlock or wizard, it's a bit redundant and he'd probably be better saving the slot. If not, then it's just nice to have a familiar in the party.

Another use of a familiar and one of my favorites is having a bat to alert you to any invisible creatures trying to sneak up on you and telling you exactly where they are for faerie fire.