I'm failing to understand what the point is of all the different sizes of needles/tips for HVLP sprayers. The needle to tip gap is adjustable (at least on my Earlex 5000) from wide open to pretty much closed. It seems to me that this adjustment should allow just about any fluid viscosity and flow rate that you would ever want besides maybe really thick latex paint or epoxy. What am I missing? Could someone please try to explain this to me?

Besides my inability to understand this, there is an underlying reason for me asking this question. I removed my tip to clean it and upon reinstalling it, the tip cracked because the needle got stuck somehow and I forced the tip on with the wrench which cracked the tip. I learned my lesson on that one...always install the tip before the needle to avoid this. Now I need a new tip. The 2.0mm needle/tip that I have been using has worked just fine for what I have been spraying (stain, shellac, lacquer, etc.) so I'm wondering why I would ever want or need any other size tip.