If landlords think it is no longer a good investment to rent, then there will be a lot of properties put on the market or kept empty. Good for new buyers, bad for existing owners as prices fall. Bad for people who cannot afford to buy or do not want to buy, as explained above.
If more landlords are attracted to renting, then more new homes will be built as builders can sell them more easily. More homes available to rent means landlords compete for tenants and rents fall. And, as I said, more homes get built.