When to prefer formatValue over formattedWrite?

[Per Nordlöw via Digitalmars-d-learn]

Is `formatValue` also preferred over `formattedWrite` when 
writing a single value?

Code example:

import std.array : appender;

auto writer1 = appender!string();
writer1.formattedWrite("%08b", 42);

auto writer2 = appender!string();
auto f = singleSpec("%08b");
writer2.formatValue(42, f);


Is `formatValue` more lightweight to the compiler?