I find it helpful in understanding changes to Code sections to use track changes to readily see what was removed and what was added. And when the text of the public law says something like replace "(B)(ii)" at paragraph (d)(1), it is difficult to picture that in your head and you might make a mistake in figuring out what the change does.
I've done this with past public laws such as the TCJA and IRA 2022.
Here are a few for the OBBBA:
Section 36B with various changes to the Premium Tax Credit but not the one many folks were hoping for to make permanent the removal of the requirement for a PTC that household income cannot exceed 400% of the Federal Poverty Line. Perhaps Congress will do this before 2026. Otherwise, many people will see their health insurance costs increase and many will drop their insurance. With fewer in the insurance pool, costs for everyone is likely to go up. Why did Congress put this limit in the PTC to start with? After all, about 60% of employees get a great tax break by being able to exclude the health insurance premiums their employer pays and there is no requirement for this exclusion that one's income has to be below 400% FPL (which is about $62K for a single person). Also, even individuals eligible for the PTC might not get it if based on their age and zip code and the §36B affordability factors, they may be found to be able to afford a second lowest cost silver plan. Again, harsh since there is no affordability factor for the exclusion for employer-provided health insurance.
Section 68 with the new limitation for itemizers in the 37% top bracket starting in 2026. There have been proposals in the past for further cut back such as to provide that the savings from itemized deductions can't be more than 25% or 28%. This cut back to 35% is not much.
Section 163(h) with change to the mortgage interest deduction and new temporary interest on domestic car loans. It is odd that they put the car loan at Section 163(h)(4) thereby splitting the mortgage interest rules that are at 163(h)(3) and (5). I already posted comments on the car loan provision that likely won't get a lot of use for the target group based on income and given the tremendous difference in price between new and used cars and domestic versus foreign, and the small tax savings from the interest deduction.
Section 163(j) with return to calculating the interest expense limitation threshold by adding back to taxable income, depreciation, amortization and depreciation effective for tyba 12/31/24; and some other changes effective for tyba 12/31/25.
Section 170 on charitable contribution deduction with a few OBBB provisions making changes.
Section 199A on the qualified business income (QBI) deduction with key change being making it permanent at the same 20% rate (House proposal for a 23% deduction is NOT in final legislation). A minimum $400 deduction if QBI from active business of at least $1,000, starting after 2025. A few modifications due to §68 limitation on overall itemized deductions.
Section 461(l) on excess business loss of noncorporate taxpayers is made permanent (it was already in the law through 2028). Minor modifications on inflation adjustment.
Section 1202 on gain exclusion for noncorporate holders of qualified small business stock. The holding periods, maximum gain exclusion and size of the C corporation are changed.
Hope these are helpful.