This post on moving from Squarespace to WordPress reveals a few interesting tidbits that were new to me. Apparently Squarespace makes changes to the photos you upload (renaming and even disabling search engine optimization, according to Scott Kivowitz). Yikes.
Scott says the move was “a pain” because plugins recommended for importing content to WordPress from Squarespace did not work as expected. Part of this falls on Squarespace for the export, but seems like plugins aren't fully stable on the WordPress side either. Hopefully this improves in the future as migrations from Squarespace will likely continue.
Ryan McCue's WordPress Importer revamp project is hugely important for better onboarding folks to WordPress.