The only possible benefit I can see to Russia (or their allied rebels) deliberately downing the plane, would be in an attempt to try to make it look as if the Ukrainian government had done it. I.e. to use it to discredit the other side, and perhaps cause them to lose some level of international support.
But, my 2 cents is that is probably unlikely. It would be a very extreme and despicable act to commit, just for the sake of 'dirtying the name of your opponent'. Also, there seems to be a lack of suitable planning that would accompany this, seeing as the investigation seems to have fairly clearly linked the incident to a Russian-operated missile. Russia is not usually so careless. If it was deliberate, I would expect them to have made more of an attempt to frame Ukraine, by using a similar missile to the ones Ukraine uses, or even capturing and using some of their equipment.
So, I suspect it was most likely not deliberate, but a negligent mistake caused by the Russian-backed rebels not properly verifying their target. Of course, following the incident, Russia has been scrambling to deflect and obfuscate, so as to save face and avoid their allies being painted as reckless and irresponsible (and themselves being irresponsible in arming/training them).
(Please note that this is mostly speculation, based on what I have seen/read in the news. I haven't read the whole investigation report.)