-In the short term, if you need Iruka, it's worth using the refine functions to get to him, and even get him to 4* or 5* without spending coupons.
-Not too sure how the timeframe is for other skill-breaks, but if you do some research, and you would wish to skillbreak them in the future, save the fragments.
-If you are going way longer term, and wish for Naruto 9 tails chakra, you can just gun for that. Main character frags have little use else other than refining (as far as I know!).

You can keep saving until you have (close to) enough to either get iruka or upgrade his star. So say if you are at 0 frag 4*, that means save enough for 20x3000=60k points before refining, or perhaps start at 55k since you can only exchange for one set a day, and the remaining 5k will take you the 20 days or so.

This way, if a new breakthrough is released in the mean time that you would use, you can get that.
If not, it doesn't really affect the time at which you get iruka so you don't really lose out.
This will effectively delay the time at which you get the seal/summon scroll, but those aren't all that important.

As long as you are sure you are not going to skill break said ninja, I do believe you can turn his fragments into points without hesitation.

That being said, if you do not care about getting to Iruka right now, you might want to wait with using the medium refining, it may be soon, it may take months, to be honest I have no clue whatsoever when it will be added, but the refining rewards will be boosted in the future.

It's all about how patient you are and how much do you care about such things. Now, I do not remember exact boosts, but for sure it does increase the number of seal scrolls and summoning scrolls you get per refine, as well as add few more potential items.

I have no info about the points being reset when it's added, so as I said I believe you may just turn them into points right now, but if you are worried about that, you can keep them for when the time comes.

There are zero ways in the common player lifetime that he will be able to gather 750000 points from refinement to get the missing 50 fragments he misses if he paid for jonin medal to get that naruto to 3 stars since at 2 stars is totally useless. And even if he is a full free to play player there are almost the same close to zero chance to gather the 450000 points needed to buy the 30 fragments to recruit him. Overall going for it is like selfshooting your feet since you also get in average less scrolls.

You only lose out on 2 seal scrolls and 4 summon scrolls. :x

No, you lose 2 seal scrolls or 4 summon scrolls for every 15k used. In the 750k perspective you lose 100 seal scrolls or 200 summon scrolls. Is not a little difference.

i think the important question here is... which fragments? some ninjas get skill books, some dont... so you should save hte useful ones and throw away hte others, which ones do you have large amounts of?

Well, won't the ninja skillbooks be obtainable through other methods than ninja frags? Or am I being dumb. Anywaya, I don't know how the refine rewards will be changed, but I recommend refining to get Iruka up to 4*. As from what I can remember, if you're not gonna use any of the skillbook ninjas, refine their frags. Btw, Hinata is one the ninjas to NOT get a skillbook. So refine her frags. I think?

you can buy the books for coupons in events mostly, you cant guarantee you will get hte one you want, also login monthlys give books when a ninja wiht them come sup

i reply under the assumption that a player is f2p, that means that in most cases that a specific ninja who can become skill broken may be useful to them at some point, because skill broken ninjas are strong, luckily the even strong skill mutations(doesnt use fragments) that comes later are even stronger, its a subjective slope as to what a player should do in this regards

so id say... check out the information available on skill breaks and mutations, decided if you want to use that ninja when its available, if yes save for it, if no refine its frags, as an example, im saving for itachi, gai and kimmimaro

hinata doesnt get skill books, this is correct for the moment, and though iruka is a useful ninja at the moment, hes not as viable later, we have an odd advantage in that we are copying a previous exisitng version, a free player should look to utilzie all the information they can to get a team they like and enjoy with ninjas they want to be effective and still be viable < idealistic i know...

I guess you DO bring up valuable and good points.

I know this already they were simply listed. :p

let exchange to Iruka dude :)