Yes, even when owner plans to occupy one unit or 3 units.
Here is why, the RIPA form covers Tenant deposits and Lease Contracts.
It protects the seller and the selling agent.
These terms are not covered in a regular CAR purchase contract.
It also protects you.
Remember you can always call CAR Legal.
It really depends on how how saavy your client is. I don't like the RIPA but in a 4-plex there are circumstances where it may be the preferred contract. The first person to ask is the lender, thay may want one over the other.
I base it on the experience of the investment client. The CAR-RPA is probably enough with a reasonably experianced investor since they will know what they are looking for and have other properties to evaluate and compare with.
Recently I saw a property that was marketed as a four-plex. But upon review of how it is classified by the city, it's actually a single family home with three unpermitted/non-conforming units. Red flag!