I've been thinking about this for a long time, but I have not found it discussed anywhere online. In some styles and/or dojos Aikidoka (uke and Nage) practice with fingers spread wide apart. I once heard this explained as holding your hands "kokyu". To me this is a disaster waiting to happen. There is a high probability in a fight of getting a lone finger caught in clothing or something and getting it broken. The fighting arts I have had exposure to emphasize keeping fingers together as much as possible for this very reason. In addition, when I rock climb, I have much more finger strength with my fingers together where they can support each other than when they are spread, which would seem to support the fingers together mode in an art with so much grabbing.
So my question is this, why do so many Aikidoka specifically emphasize spread fingers?
Your concern here is that of hurting yourself. This is, indeed, one of the ways of being hurt in a real fight.
However most adversaries won't have enough presence to take advantage of taking hold one of your fingers and break it.
The typical way of hurting yourself can happen, anyway, also with tightly closed fingers: a fist. You throw it, and you hurt an object instead of your adversary and you get a broken knuckle, a broken thumb, or a mild cut that anyway, being the anatomical (if that's the correct spelling in English) structures so superficial, cuts one of your tendons and makes part of your hand/fingers unusuable, normally in extension (that is: you cannot open
it anymore, involving one or more fingers).