Q.Why Do You Plant Some Plants in Hills?
I have some plants, such as cucumbers, in without hills with good results. My wife says they should be in hills. Why?

Certified GKH Gardening Expert
Hilling is a practice that is not really recommended anymore. It has become a garden habit that is more a personal choice than a "have to do it".
The benefits are that it was thought that the hill would make the soil a little warmer and a little drier. It is kind of like a tiny raised bed in the garden. But, if you are already growing in raised beds, the benefits pretty much go away.
The negatives are that the hills can dry out, leaving the seedlings with too little water. Even later, water can run off the hills rather than being absorbed into the soil of the hills. They also are a bit more susceptible to certain kinds of pests.
Really, what it comes down to is what works best for you. If you have not had any trouble growing vining plants at ground level, then keep doing that.