I also manually input all the data. It forces me to think more deeply about precisely what I am doing. Too much automation removes the taxpayer from the equation. In my view, taxes should not be a black box; you should know exactly how they are calculated and exactly where the data has come from and where it is going to.
I used to do this, but I (somewhat) refuse to do it now. I will still review the tax forms before filing, but I'm fine with "it's good enough."
<rant>
I had an issue this morning while filing. I had two 1099s for company stock (ESPP/RSUs). These all have an adjusted cost-basis. I downloaded the transactions, because I'm not going to enter 20+ entries (I used to do this manually, but no more). I update the cost basis for each transaction and double-check to make sure everything looks right. When I go to file, TT complains that I haven't entered an adjustment amount in the Capital Gain (Loss) Adjustments Worksheet.
I check and the first 1099 only has 'B' coded and the second 1099 has 'BN.' Why the difference between the two 1099s?
So I spent an hour reading IRS tax forms trying to figure this out. Time not well spent.
I figured it out, I think. The problem is with the 'N'. I went in and enter '0' for the adjustment in Part II Manual Adjustments, since I specify the corrected basis in Part III Specific Adjustments.
This is time I won't get back. I figure even if I did it wrong, it's a minor infraction and odds are I won't hear from the IRS.
I explain to my European family on what we have to do to file taxes in the US and they don't get it. Paying taxes should be a non-event, not the yearly tradition that we have in the US. Unfortunately, like many things in the US, filing taxes is a business that is driven by third party financial interests. I'm more than happy to pay my fair share, but they shouldn't make it this difficult.
</rant>
Going back to the TT part, I always skim over the actual forms before submitting. Due diligence and I want to make sure that TT doesn't do something stupid.