Paint manufacturers have thinning recommendations just as they have recommended application thicknesses to achieve a dry film thickness sufficient enough to warranty their product. If you can't achieve that thickness you have no warranty. Might not be a big deal for a diy'er, but as a Painting Contractor of 35 years, there's certain guidelines which need to be satisfied so we're not on the hook for labor and materials should things go sideways. When you add excessive amounts of thinner, you reduce the overall film thickness, which requires more time & material to apply more to achieve the same. However, if you want to thin your products 50%, go for it.
As an aside, there are other ways to lower viscosity without sacrificing the overall film integrity...
-Heat up the paint. For every degree above 70°F, it's approximately the equivalent of thinning your product 1%, and most paints can be safely heated up to 90°F without damaging the paint.
-Use flow enhancers and levelers. Penetrol for oils is old tech, it will yellow white paints and it reduces sheen, so with oils, use Corotech Brushing reducer V701 or Interlux Brushing Liquid 333. For water-based/waterborne products, use BM's 518 or XIM.
-Remember also that generally speaking, over-thinning will change the actual chemistry of the product because excessive amounts of thinners will actually begin to dissolve the structure of the paint film. One noteworthy exception would be mineral spirits in oil, since you could literally thin it with up to 100% mineral spirits and it could still actually form a complete paint film after curing, (albeit a much thinner, weaker film).
And to address your concerns regarding not being able to achieve a good spray pattern without excessive thinning...
-Turning up the pressure on your sprayer could certainly help produce a finer pattern. I know the ultimate goal is to spray at the lowest pressure possible while still producing a good spray pattern, but some products require higher pressures at the gun to atomize fully.
-Using a larger spray tip will spread the pattern out further and help minimize "fingers" in the spray pattern.
-Use a different rig & equipment. The Binks Super Bee was a great workhorse used by many painters every day, but that was over 30 years ago. Advancements in spray technology have been substantial in that time. The low end deadband of sprayers are nearly non-existent on pro-level rigs. Fine finish low pressure spray tips have been one of the most important advancements for architectural coatings in decades. Graco's are fine, but Tri Tech's are better.
