Originally Posted by Psychocycles

I own 105 5800 & Ultegra R8000 - shifting at the rear is difficult to tell the difference, but the front shifting is noticeably better with Ultegra. This could mean the difference between catching the wheel in front and getting dropped in a race after a climb in the little ring, so I pay the premium for Ultegra (hard to justify DA for now, but I'm also not getting paid to win races). It's all relative, and I wouldn't say that it's a scam. Difference between Ultegra and DA (R8000 & R9100), though, is much smaller than that between 105 and Ultegra, as Shimano described themselves.

If for your purposes 105 is sufficient, and I would wager that for the majority of cyclists it definitely is, buy 105 and remain happy, and let others buy DA. I personally love when older, richer people buy DA because as others mentioned, that pays for R&D so that the high end tech from 3-4 years ago trickles down to Ultegra/105 level.