I achieve pretty consistent and satisfactory results with my current technique but would like to hear what others have to say.

I am using a Vario grinder and Quickmill Vetrano 2B.

Here's my question; I typically grind fairly fine and use a light tamp. If I used the standard "30 lb. of force" tamp I'd choke my machine. My extractions are pretty nice, though it is not unusual for them to run long. I'd prefer a slower extraction than a faster one, if I wasn't hitting the 25-30 second window. My question is what would be different if I coarsened the grind and tamped more firmly. Obviously, if I'm grinding fine, then the water is extracting from smaller coffee particles. If I were to significantly coarsen up my grind, to where a 30 lb tamp pressure would work, the particles would be much larger and the extraction would be very different.

Perhaps either way is "right", since either way can provide good results. I am getting satisfactory shots, but I'm curious about the principles of extraction and how they might apply given my current technique.

Any thoughts or advice would be appreciated.

Are you weighing your doses to 0.1 grams each time?

It is generally recommended that you always tamp the same way and modify the dose and grind to suit the coffee and your taste preferences. Anything over about 30 pounds will have the same results unless you are using a bung hammer in conjunction with the tamper. After about 35 pounds the coffee will compress further so little that the difference between 35 and 50 pounds is negligible.

I can think of two exceptions:
1 - If you need to use some specific tamp force (either high or low), you are likely compensating for some other problem. Sometimes that is necessary such as with (like an under-performing machine, crema enhanced portafilter, stale coffee, a grinder that creates a lot of dust, pre-ground coffee, etc.).

2 - I have read for manual lever machines a light tamp and fine grind are beneficial.

Randy, what you are saying makes sense. And what Mark is saying is also something I have thought about, small grind size giving different flavor profiles than larger grind size. I have read somewhere, possibly on HB, about Italian baristas using a light tamp on their grind. There are times where my beans change enough for me to adjust the grind size, and out of laziness I just adjust my tamp pressure to compensate for this, right or wrong is not something I care too much about. Most of my drinks are milk based, which may cover up any flaws I am creating by doing this. I guess one way to check this is to do a side by side comparison of the two different grind size/tamp pressure to see if there is any difference.

I am no expert, so take it fwiw, but ever since I started dialing in my shots by brew ratio (weight) a great deal of my issues disappear. I can now dial in new beans and/or adjust grind settings much faster and get better results.

Right now I am doing a 1:2 brew ratio. Dosing 17g, set the scale under the brew group, brew to 34g and try to time it to 24-26 seconds. I am finding these to be a breeze and totally changed the way I have done things for the past 5 years. I only wish I learned this many moons ago, my life would have been easier.

HTH