Recs.
Updated
SpecsUpdate
Pros
Pro MusicXML import and export ensures a degree of compatibility with other programs
If you are submitting files to a publisher, MusicXML format can be read by the big engraving programs: Sibelius, Finale, MuseScore, etc. Often there are some display issues that will need to be tweaked when using MusicXML between different programs, but publishers will spend a lot of time tweaking the file anyhow.
Pro Easy inscription
The newest version of MuseScore added collision detection for elements - so unless you're importing something really wonky, you shouldn't have text and notes overlapping or hitting each other. You can save your favorite spacing and size preferences to a file and have MuseScore automatically load it when you start a new project, or load it manually from the file.
Pro Great sheet sharing web page
So you composed a new score! Now what? Well, you can start by putting it on the muse score sheet music sharing web page where others will be able to enjoy it and comment on it. Or maybe you're just looking for a score from an old video game: in that case, you should probably search the page for it, and download one of the many available formats (pdf, muse score format, mp3, xml, etc).
Cons
Con No real-time transcription tool
If you are looking to play your MIDI keyboard and have the computer attempt to transcribe and print out your latest masterwork as you play, MuseScore is not the tool for you. It does, however, have a "semi-realtime" note input mode, which is kind of the same thing as a transcription tool.
Con Bad support for microtonal music
Although Musescore does offer in addition to the Western 𝄫/♭/♮/♯/𝄪 accidentals also nonstandard ones, but they are essentially just glyphs; MuseScore does not know how to resolve them or use them in key signatures, let alone offer proper tuning of the playback pitches. (Playback pitch can be set manually in cents, but this is very cumbersome and error-prone.)