Here's a good breakdown thanks to
this NeoGAF thread.-Sega is continuing their refocus to digital games.
-As part of this, they're downsizing their Western publishing business (but not their Western development studios), and staff in their arcade game department in Japan. They're also transferring the staff they can to mobile/PC Online in particular.
-So far 120 layoffs have been announced at Sega West, primarily in Sega of America and some in Sega of Europe (this is the publishing business, not the studios).
-Sega intends 300 layoffs total, with a notable portion of that presumably coming from the arcade business in Japan.
-They're plausibly also changing what some of their staff work on - and we've certainly seen that over time from Sega - but that's not directly related to the layoffs we're talking about today. The layoffs are focused on business components that can't easily be transferred to digital, which are primarily retail publishing resources and physical devices like arcade machines.