We were sitting around the table after x mas dinner. Someone asked why some guns have a right hand bolt but a left hand ejection port.I read somewhere that benchrest shooters use them but we could not figure out what the advantage would be.

Would be great for single feeding off a rest. Operate the bolt with one hand and feed the ammo with the other.

I believe that it might have more to do with ease of loading than it does with ejection.

A popular configuration for some benchrest shooters is a "dual port" action. RB, LP, R eject. They are fun to shoot from the bench, the fired case just disappears (falls out on the bench) when you pull the bolt back. Insert another round, close the bolt and fire.
Jerry Stiller has a patented action called the "drop port". The fired case falls out the bottom when the bolt is pulled all the way to the rear. The next round is inserted in the L port and you are ready to close the bolt and fire. The hole for the fired case has a profile much like the fired case. I think that this configuration is only used on BR rifles that are chambered in very short cases like the 6 PPC, 6BR and variants based on those cases.