I can try to give an example:
I have a class that samples the mesh at a given interval and stores it, effectively creating something like this for an animated object:
The code for the class is here: http://pastebin.com/tUQaAn18
If I remove the check "if (frame != prevframe)" I get some weird results.
Consider a box that moves along one axis in linear speed, and is sample every other frame:
Example 1 is where I check if the input frame is the same as the previous frame.
Example 2 is without the check. You see that example 2 samples the box more often.
Here is my modifier setup:
All the input values are integers.
It might be just an error that I've made, so I tried to show my approach to it.
