One clear benefit is decent GPU performance, without the cost, physical size, and power/cooling for a discrete GPU. It's way faster than Intel or AMD's integrated graphics. You can see this difference when you unplug a MBP vs any of the laptops with a discrete GPU.
Marketing brags about memory bandwidth based on clockspeed * bus width = 400GB/sec. Getting 60% of peak on some memory bandwidth benchmark is pretty common. Try McCalpin's stream benchmark on your platform of choice to verify. I suspect you'll find similar on Intel or AMD on desktops, laptops, or servers.
Not sure I buy the memory bound argument, sure peak performance will not change, but worst case performance can be caused by cache misses. So I expect that the new MBPs will be more evenly fast than the x86-64 competition, even while doing stressful things. I don't currently need a $3k laptop, but am hoping they ship a mini with a M1 Max or Pro.
To quote anandtech:
The fp2017 suite has more workloads that are more memory-bound, and it’s here where the M1 Max
is absolutely absurd. The workloads that put the most memory pressure and stress the DRAM the
most, such as 503.bwaves, 519.lbm, 549.fotonik3d and 554.roms, have all multiple factors of
performance advantages compared to the best Intel and AMD have to offer.
So an apple M1 Max is 19% faster on SpecFP (floating point applications) as a Ryzen 5950x which has twice as many fast cores (16 vs 8) and runs at 105 watts TDP. That's pretty amazing in my book.