Also. Losing a lot of money? That is such a 1995 way of looking at it. The goal as an nba player - -with the rookie scale -- is to get to free agency as early as possible. Think about it. No more $90M deals for being a No. 3 pick or something.
Because of that, if you have guaranteed first-round money, you take it and then play 3 years for your next contract. The NBA is picking up the development tab. Second rounders? It is a host of foreign guys, older players, and weird players.
Now, if you are projected as a late first, be careful. You slip into the mid second round nothing is guaranteed. And worse, you are so cheap they can cut and trade you as chattel. If there is any conceivable way he drops to second round, he should come back. But does it matter guaranteed, $3M vs. $1.8M? Not when you factor in the year of service you gain (closer to FA). He'll make up whatever he lost by not returning hitting FA a year earlier than if he stayed.