I user the suffix field for titles of nobility, but not everyone agrees or sees the point.
There are at least two different "standards" that come into play.
1. An encyclopedic standard, in which the "suffix" is for disambiguation. So, (Sir) Thomas Howard, 3rd Duke of Norfolk.
2. An birth name standard, in which the suffix is omitted except where it forms part of the birth name (Jr., III). No, post-nominal initials. Thomas Howard (above) has to be plain Thomas Howard.
Set these against an older genealogical standard that was a blend of the two. In the old days, if I were typing a family group sheet for this Thomas Howard, his name would have been the same as the encyclopedic standard -- (Sir) Thomas Howard, 3rd Duke of Norfolk. Unfortunately, modern genealogy software has lost sight of the differences so many younger genealogists aren't aware there was ever a way of doing it other than the way the software does it.
Then, here in Geni many people use a "modified birth name standard". That is, they won't use the suffix for actual titles but they want to use the suffix for knighthoods, academic degrees, etc. Often, they also want to use Jr., Sr., and other numbers that were never part of the person's legal name.