A bird in the hand is worth two in the bush.
And and Infantry on your front line is worth more than 3 IPCs income for next round.
What can you buy with 3 extra IPCs? Another Infantry. And where will it be? Back home. So it’s a quick way to transport an infantry back to Germany, but I’m usually trying to move them the other way!
Also, you don’t really deprive Russia of the income, because when Russia recaptures they still get the income anyway. In the end, it amounts to an even trade, the question is who can afford the trade.
That said, I will put a picket if it prevents the other side from blitzing my AF or something like that.