I always feel safe to thin the flowers of certain varieties and species just to accelerate the thinning process and direct as much energy as possible where I want it. For apples, Braebern is certainly a candidate for flower thinning- the tree is so spurry and prone to bienniel bearing (for me). Goldrush is another I thin the flowers of. Any peach tree I grow can be thinned at any time and so on.
I would thin Asain pears early as well but their flowers are extremely frost tender so I wait until shortly after bloom to begin although I often thin the spurs a lot when I'm pruning.
The reason I like thinning early is also to limit my contact with Imidan as I do all my thinning by hand. It's just too complicated for me to thin apples chemically because the orchards I manage are small with a wide range of varieties that respond differently to chemical thinning. I also hate adding Sevin to my program because it seems to assure outbreaks of mites.
[NAFEX] Braeburn blossum thinning,
Alan Haigh, 05/03/2009