For a few years I've been running with a 5mm heel lift in my right shoe and also Superfeet inserts. In March I picked up a new pair of shoes, the same brand/model/year that I had been running in. I also got a new pair of Superfeet at that time. What I forgot was to put in the heel lift and this launched the accidental experiment.
I by the time I hit 200 miles in those new shoes, my right heel was causing me a lot of pain - plantar fasciitis. My left hip was getting sore too. I assumed the two things were related and decided to get a new pair of shoes. They didn't seem to help much so I started some plantar fasciitis treatments such as rolling my foot on a ball. That was making it somewhat better.
Three weeks ago I was getting a spare pair of shoes ready for a race so I pulled my old Superfeet inserts of my winter shoes. It was then I noticed the heel lift. I had forgotten about the lift when I bought new shoes in March and hadn't been wearing it for almost 3 months. Since then I've been wearing the lift in my work and running shoes and my plantar fascittis is almost gone.
So, for me, the 5mm heel lift can make all the difference.