Trichoplax suggested a number of advantages to providing binaries, but no disadvantages.
Clearly, the largest advantage to providing binaries is the high probability that this will increase the size of the user-base. The type of person who visits this site is technically very savvy, most likely with programming experience, and likely to prefer to download source and compile it.
But we are actually a very small subset of the number of people who use computers and browse the Internet. Most users do little more than browse the web, chat on Facebook, send emails, etc.
Chrome and Firefox have displaced Internet Explorer as the leading browser, helped by having alternatives to Windows as a platform. But how successful would this have been if every potential user was required to download the source of Chrome (and webkit!!) and compile it from scratch.
But success comes at a price (one which can kill small FLOSS projects), literally a dollars and cents price.
Hosting sites like GitHub often have limitations on the size of individual files. And you really don't want to save large binaries in a Git repository. These sites also have limits on the amount of traffic that a given repository should generate.
This means you will need a host site which lets you publish potentially large binaries (multiple versions and multiple targets). It should also not be bandwidth limited. This costs money, which the project owners will need to raise from some source.
Too many platforms
Having bitten the bullet, and set up a server, you need to decide which platforms you will support. And which versions of those platforms
- Windows Vista, 7, 8? One or all?
- Which distro mechanisms of Linux? (rpm, deb, ppa, etc)
- OSX native, or Homebrew?
- Android, iOS? Which versions?
Does the project have access to contributors that can support all the platforms you want to distribute for? Do you have people who can test the provided binaries to ensure they actually work?
Security and Liability
Okay, it's all taken off .. you have a distribution mechanism, binaries, and lots of users.
- How do you prevent the insertion of adware (a la Sourceforge) if you aren't using your own servers?
- How do you avoid trojan injections (there are commonly adopted methods)
- Are you legally liable if someone downloads an infected executable from your site?
- Do you need some liability insurance?
High numbers of lower-skilled users
As your project (assume it's a complete application) attracts more and more 'average people', you will be held to a higher standard for support.
- Do you have good user documentation?
- Will you provide translations for other (human) languages?
- Do you now need a bug tracker hosted on a larger site?