You can take a discount code from playbill.com, theatermania.com or broadwayabox.com to the box office. This will save online fees.
It really depends on what show you want to see. The problem is, since the pandemic, those sites just aren't offering as many or as good discounts as they used to. This minute, playbill has discount codes for 3 Broadway shows and theater mania for 5. If you want to see one of those shows, great. But the TKTS booth typically has many more shows available. The negative is that you have to go to either Times Square or Lincoln Center and possibly stand in line.
Of course, some shows like Wicked, Hamilton, the Lion King and Merrily We Roll Along don't usually discount, so they won't be available at any of these locations.
It is a balance of cost and convenience. I see a lot of shows, so TKTS tends to make the most tense for me 90% of the time.