It requires (electrical) power. I don't think this could reasonably be called "friction". When I think "friction", I think of burdens imposed on users. Bitcoin has relatively few of those.
There are about 500 transactions per block; each block contains 25BTC + fees (the fees are negligible at the moment). At the current price of $350/BTC that means that the revenue per transaction is 25*350/500 = $17, which means that the cost per transaction should be around that area. This means that the low transaction fee is actually massively subsidized by the fixed block reward.
It requires (electrical) power. I don't think this could reasonably be called "friction". When I think "friction", I think of burdens imposed on users. Bitcoin has relatively few of those.