Valine is one of the three branched chain amino acids, although infrequently tested in isolation and possibly the least important BCAA for body composition and does not appear to have any known unique benefits associated with it.
Valine is most often used for
In isolation, there is currently no hugely significant benefit of valine supplementation that cannot be replicated by either leucine or isoleucine supplementation (as the possession of a 'branched chain' itself confers some bioactivity, but this is shared to a degree between all of the BCAAs). This may simply be due to lack of evidence, as many time when valine is researched it is in studies that merely want to test the effects of a branched chain amino acid (and valine is randomly used) and the bioacitivies of valine just haven't been purposefully investigated much.
It seems to be more similar to leucine than it is to isoleucine, but the transient state of insulin resistance occurs faster than with leucine (isoleucine causes glucose uptake) while the muscle building effects of valine are likely less than both leucine and isoleucine.
There is currently insufficient evidence to suggest an optimal dose of valine supplementation and for what purposes valine supplementation might actually be useful for.