The September 21st Fernandina Beach News-Leader had this article on page 3a, by Eric Gutierrez.
Florida is a closed primary state, until 2000 you only vote the ticket of your registration or nonpartisan contest. But in 1998 Floridians approved a constitutional amendment opening primaries to all voters, via Universal Primary Contest, if all of the candidates are from a single political party. Thus in a primary if there in no opposition from a recognized party it is designated a Universal Primary Contest and all registered voters can vote.
Two years later, then-Secretary of State Katherine Harris issued an opinion that said the existence of a write-in candidate was enough to cause a primary to be closed. It has been used to game the system ever since.
If you are a Republican or Democrat facing only opponents from you own party you have to worry that voters from the other party will vote against you. You can eliminate this by having a ally register as a write-in candidate, thus creating a closed primary situation.
In this case Justin M. Taylor faced two other Republicans primary candidates; Klynt A. Farmer and Joe Zimmerman and without Don Tanner opposition as a write-in it would have been a Universal Primary Contest open to all registered voters in the district.
Was Don Tanner someone who intended to run as a write-in in the general election, but has for some reason decided to withdraw, we will never know. Was he an ally of one of the other candidates or just a loyal Republican, we will never know. Was he an ally of Justin Taylor, again we will never know, but the optics are not good for Mr. Taylor.
In a primary where the winning margin was 681 votes (4.4% of total vote) would the outcome have been different if it had been a Universal Primary Contest, likely.
It should be noted that this was the only County Commissioner race with a write-in candidate.