Davidski at Eurogenes points out some problems in the ancient DNA evidence with the hypothesis that the Northern and Central European Bell Beaker people are derived from the Hungarian Yamnaya people. There are lots of archeological and geographic reasons why this hypothesis is plausible and the autosomal genetic evidence isn't inconsistent with this hypothesis, but the ancient Y-DNA data doesn't really support this conclusion so far.
We care because the Bell Beaker people were the last major wave of migration into Northern and Western Europe (in the late Copper Age and Bronze Age) before the gene pools in those regions came to be very similar to those of modern Europe. The Bell Beaker people are also notable because many people believe (although I am somewhat skeptical of the claim for reasons beyond the scope of this short post) that the Bell Beaker people were the original Indo-Europeans in this part of Europe. At any rate, the Bell Beaker people without a doubt were very important in causing the people of Western Europe and Northern Europe to become the people that they are today.
We know, in very general terms that the Bell Beaker people have significant European steppe ancestry, and we know about when they started to appear on the scene, but we lack the kind of more specific understanding of where in particular they came from and what route they took that we have in the case of many other notable mass migration in world history (especially in the late prehistoric period).