Careful foreclosure shoppers can almost always buy properties at less than full market value. The size of the discount will depend on local market conditions and your own skill, but there are always bargains to be had.
Another benefit is the fact that there is less competition among buyers for foreclosure properties than other investments. Right this very minute, if I had a three-bedroom, two-bathroom, brick ranchstyle home in a good school district and in move-in condition, at a reasonable market price, I could sell it to an investor in three minutes.
If I had twenty such houses, I could sell all twenty in a day because they make great rental houses. Those same investors to whom I sold the houses would not search out those opportunities among foreclosures. It requires too much work and involves some risk other than the normal economic risks for any investment. There is a lot of competition searching for the For Sale By Owner (FSBO) and Multiple Listing Service (MLS) rental home candidates. Relatively few investors and future homeowners, by comparison, search the foreclosures.
Another benefit is the ready-made tenant. If your strategy is to buy foreclosures and rent them to the former owners, you will probably have long-term tenants in place. Remember, most former owners were not financially irresponsible. Most of them simply fell on hard times and could not dig themselves out of the hole they were in. You have probably read other books and articles with horror stories about renting to former owners.
You should be mindful that such things could happen to you. You could also make millions over the course of a few years by investing in foreclosure houses. Neither one of those things is very likely to happen, although each is possible.