If your client qualifies for record sealing, the record of his conviction will no longer appear if someone searches the court website or the BCI database. It is as if the record of the conviction is put in a locked filing cabinet.
Unfortunately for your client, there are some entities that have the key to this filing cabinet because a criminal conviction makes a person ineligible for employment in certain fields. If he wants a job in those fields, he will need a Certificate of Qualification for Employment (CQE).
Ohio Revised Code section 2953.32 contains laws about sealing a conviction.