Hopefully one day an alvarezsaurid specimen will be found with preserved stomach contents, telling us what they did eat: [...] grubs (forelimbs used to strip bark),
Not recommended for an animal that can climb... about as well as a horse.
eggs (forelimbs used to carry and break open large eggs - and the long legs were used to run away from angry mothers),
maybe carrion (forelimbs used to tear open carcasses)?
It's also possible that the forelimbs were used for different functions in different alvarezsaurid taxa. After all, there is an impressive range of size variation in the group, from little _Parvicursor_ (maybe under 1m in body length) to _Rapator_ (possibly over 6m).