It is a free (or close to it). In no way does it hurt maneuverability. So this year he have Pique and Lenglet for sure (well as "for sure" as you get while football). We may or may not get something from Umtiti. Murrillo is a competent La Liga player on rent with an option to buy. Assuming Tobido comes of a free or almost free, that is another solid prospect and potentially able to contribute now.
To me this is VERY smart business. Leaves some options this spring, and but by the summer window hopefully have a reading on Umtiti and Tobibo (and perhaps Murrillo), if one or two looks promising for recovery (it is entirely possible Umtiti is mostly fine over the long term and this is the kind of thing many players play with--fans really don't have access to the best and most modern medical info) or high level play-- being part of a long term solution-- than that is 80-100mil you don't have to spend on a CB. If the prospects are poor, for a solution on the squad this spring than De Ligt or next next best thing is the way to go.
I am not a reflexive defender of Barca's leadership--more critical than not since Pep left--but this looks part of some smart plays in winter transfer window. Rabiot for free is also great business. If Rabiot didn't have skill and positive impact on the pitch Spurs wouldn't have gone for him, nor would have QSG had this incredible unprofessional hissy fit about a player who simply wants to leave. Barca didn't do that for Pedro, or Liverpool for Can, or BvD for Lewi, or Shalke for Goretzska. But QSG is a bunch of spoiled, classless, men who are used to so much extra, free and entitlement dough they usually can get what they want without having to treat anyone or any other organization with dignity. And if anything was going to get a spoiled 23 year old to be focused and to grow himself a bit more--prove PSG and France football wrong--I'll take that extra motivation.