ok, this is NOT a MAC or PC thing, this applies to BOTH comp manufacturers.......
anyway, an md5 is a File Integrity Che3cksum, basicially it is a bit-for-bit file checking generator, emaning it checks EVERy flac/wav/shn/whatever for a bit-to-bit comparison, for archiving, even burning to disc, i check ALL md5's, and even tho flac has a verifying checksum function built into every encode/decode, i STILL include an md5 for EVERY folder, stuff i put onto etree AND archive i include an md5 of JUST the flacs, but when i i ONLY upload to archive.org, I include an md5 of the whole folder, just for laziness/quickness i guess.........
now onto SBE's, otherwise known as, Sector Boundariy Errors, these occur when a track/song break IS NOT placed on the sector correctly, sometimes this causes a pop/click on playback. to avoid this, and since maybe 2002/2003, flac frontend has enabled fixing of sector boundary alignment on the encoding process, so i can avoid SBE's right there, and i also use cdwave to track(tho I Still get one eventually when i dont have a padder/wasted track at the end of each set, but who cares, if the end of my set is crowd and the beginning of set II is crowd, im not worried about an SBE affecting that, i have yet to hear a pop/click when using cd wave to track and flac frontend(with sector boundary alignment set) and have NEVER heard any issues with that process, YMMV
hope i helped a little bit, its alot of stuff to take in, i gave it to you in laymans terms, a real description much more technical can be found at etree.wiki or somewhere along those lines, or just search sector boundary error on google