Lukaku has always been better for the Serie A rather than the Premier League. We have proof for that considering his past statistics. 
Therefore Chelsea just signed him back for nothing. They were just fascinated with his performance at Inter and forgot about their past with him. It should be due to acting amateurish otherwise there is no way you do this.
Anyway he has returned to Italy but this time to Roma. It is a one-year loan deal though so I can't say good riddance for Chelsea. They will still have 2 more years with him in case he returns.
But let's say Roma didn't want to extend his loan and he didn't get any other reasonable offer in Europe then Chelsea can go for Saudi Arabia option for him.
Therefore Chelsea just signed him back for nothing. They were just fascinated with his performance at Inter and forgot about their past with him. It should be due to acting amateurish otherwise there is no way you do this.Anyway he has returned to Italy but this time to Roma. It is a one-year loan deal though so I can't say good riddance for Chelsea. They will still have 2 more years with him in case he returns.
But let's say Roma didn't want to extend his loan and he didn't get any other reasonable offer in Europe then Chelsea can go for Saudi Arabia option for him.