The phrase ūsus est + ablative is the rarer counterpart to the well known opus est + ablative, signifying need.
- Nunc vīribus ūsus est: now there is need of strength.
- Quid istīs cōnscrīptīs ūsust: what is the use of getting these in writing?
Ūsus vēnit is another still rarer alternative.
The Essential AG: 411