On my 2 vermeers,   there is a half link  on  all the  heavy chain.     When  the  tensioner  is maxxed out,   I'll take the half link out  and  re tension it for the rest of that season..  and  start with new  chain  next year.     

I use  cheap  farm store   #80 and 60  chain,   and  get   about  3000 bales  on the full length,  and   about 2000  after the half link is  out.   I think there is  114  links  in the  big chain,  so a half link is  about half a  percent of  total   with  the tensioner  travel,   I'm  probably close to 2%  'stretch'  when  done.

I figured  it's more important to keep the chain   in spec, to make the sprockets live.   All mine  are  still original sprockets  with    50k+  bales,  but  several sets of  cheapo  chain.