In my example there is only 1 router that is running EIGRP and RIP at the same time. When you have two routers doing redistribution, it is possible that you get a scenario like this:
Prefix from routing protocol A > B > A
This is a problem that can cause routing loops or sub-optimal routing. Imagine that we have prefix 192.168.1.0/24 in EIGRP, by default it has a AD of 90.
Once it is redistributed into RIP, it has an AD of 120.
When we redistribute it back into EIGRP, the AD is 170 (external).
Since 170 (external) is higher than 90 (internal), EIGRP will never prefer a redistributed prefix over an internal route.
RIP doesn’t have this “failsafe”…when you redistribute into RIP, the AD is always 120. We can change the AD ourselves to solve some problems.
Besides the AD, we can also fix redistribution problems with route tagging and changing metrics. In the beginning it might be very confusing to understand so try to focus on the problems of redistribution scenarios and then see if it can be fixed by playing with the AD, metric or tagging 
Rene