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    <p><code>printfn</code> and its various cousins have several advantages:</p> <ul> <li>They're <strong>shorter</strong>.</li> <li>They <em>can</em> do some <strong>static type checking</strong>; i.e. <code>printfn "%d" "bad type"</code> will not compile.</li> <li>...but you don't have to do static type checking; <code>%O</code> prints any object</li> <li>They can print <strong>"smart" representations</strong> for things like arrays, tuples, and discriminated unions with <code>%A</code></li> <li>They can be partially applied; i.e. <code>printfn "%d, %d" 3</code> is a valid expression. This is particularly nifty since the compiler can check that you actually apply the right number of arguments when you later use this subexpression - unlike <code>Console.WriteLine</code> which will happily accept too many or too few parameters.</li> </ul> <p>In practice, the most common partial application is likely to include just the format string; e.g.</p> <pre><code>let printParticle = printfn "Particle at (%d, %d), state %A, p = %f" printParticle 2 3 //compile time warning about ignored value printParticle 3 4 someState 0.4 //fine printParticle 5 6 someState 0.4 0.7 //compile-time error </code></pre> <p>However, prior to F# 3.1, it's also <strong>slow</strong>. It's plenty fast enough to keep up with you the coder, but if you're using it in some form of serialization, it could turn into a bottleneck. The <a href="http://blogs.msdn.com/b/fsharpteam/archive/2013/06/27/announcing-a-pre-release-of-f-3-1-and-the-visual-f-tools-in-visual-studio-2013.aspx" rel="noreferrer">F# 3.1 release announcement</a> (which is distributed as part of Visual Studio 2013) claims to improve the performance dramatically, though I have not verified this.</p> <p>Personally, I usually use printfn for exploratory coding, and then I largely stick to <code>%A</code> with the occasional other specifier thrown in. However, the .NET native string formatting is still useful in some cases for its detailed culture and formatting-related options. If you want maximum speed direct concatenation (or a <code>StringBuilder</code>) will easily outperform both as this avoids interpreting the format string.</p>
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    1. COThank you for a very clear and useful answer. If you could elaborate on the "partially applied" part, that'd be even better!
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    2. COI agree that `printfn` and related functions should generally be used instead of `Console.WriteLine()`, but it's worth mentioning that they're also relatively slow (which may matter for some use cases).
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    3. COI didn't know that, thanks for the update - I guess I never tried to use it for huge amounts of data :-) updated!
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