Holy cow, I wrote a book!
In Microspeak, fit is a predicate noun
which is never used on its own but always comes with a modifying adjective.
For something to be a good fit is for something to be
appropriate or suitable for a particular situation.
The opposite of a good fit is not
a bad fit, because that's pejorative.
Rather, something that is not a good fit is referred to as a
The purpose of a previewer plug-in is to allow users to view
the media without opening it.
An image editing tool
would not be a good fit for the previewing feature.
(Alternatively, "would be a poor fit for the previewing feature.")
To be a good fit with a particular group is to mesh well
with that group's existing practices and conventions.
The Datacenter Edition of the product is a poor fit for most small businesses.
The group in question need not consist of people.
The results are obtained incrementally, which makes it a good fit
for IQueryable<T> and LINQ.
Microsoft Human Resources loves to
apply the concept of "fit" to people fitting into a job position.