The main (at least initial) advantage to keeping Cristall around is how much they still need high level skill and creativity. If this were still a bonafide offensive powerhouse it would be a different story. They could afford to pick apart his more evident weaknesses (strength/battles) and decide he's not fully ready yet. They still may go in that direction but the lineup's overall unknown offensive quality should IMO lead to continued initial opportunity. There are a lot of new faces and their timing should only improve...but they're still probably not very dynamic offensively. They still haven't added a true headliner type talent. They should be better defensively, in theory a stronger possession team and that should lead to more sustainable success. But we'll see.
Outside of Ovechkin and Strome there are question marks all over the top nine in terms of level of play and productivity. I'm skeptical Cristall sticks the whole season but as an initial reward for his growth/determination and to fuel further competitiveness for spots it makes sense to keep him around for now. Ultimately it's still tough to figure he's up for the six month grind of playing against men. That battle level would either need to come up considerably, he'd need to pack on more strength in a hurry (while sitting initially perhaps) or he'd need to be dynamite offensively to compensate for the limitations. He does possess attributes that they're thin on...playmaking, skill and offensive sense. Minus Backstrom, Oshie and Kuznetsov they need to foster those new silky smooth attackers as best they can. Cristall and Leonard on the horizon and then Parascak perhaps a year later should at least put most everyone in the middle six on notice that mediocrity won't cut it.
The biggest positives early on I think is the back-end when healthy and PLD. Again, we'll see what it looks like against strong teams. Their schedule at the start is stiff: vNJD, vVGK, vDAL and
@NJD. Some home cooking but right into the fire.