Dates we need to ignore

I set up the usual start, finish (better than ES,EF) and then the Later Start, Late Finish.  For simple things like my Start Milestones that have ACTUALS, I get a value in the Late Start and even worse gives me a big float bar.  There should be no float on an ACTUALIZED Activity.  So this is just data we have to ignore? Where does this date come from / what does it mean? I assume some people set up UDF fields and just copy the remaining work to be less complicated for novices but this seams so strange it makes me feel I am not setting up correctly. I used P3 for so long, sometimes the differences still confuse me.