This option changes the size of the buffer that Git uses when pushing
data to a remote over HTTP or HTTPS. If the data is larger than this
size, libcurl, which handles the HTTP support for Git, will use chunked
transfer encoding since it isn’t known ahead of time what the size of
the pushed data will be.
Leaving this value at the default size is fine unless you know that either the
remote server or a proxy in the middle doesn’t support HTTP/1.1 (which
introduced the chunked transfer encoding) or is known to be broken with chunked
data. This is often (erroneously) suggested as a solution for generic push
problems, but since almost every server and proxy supports at least HTTP/1.1,
raising this value usually doesn’t solve most push problems. A server or proxy
that didn’t correctly support HTTP/1.1 and chunked transfer encoding wouldn’t be
that useful on the Internet today, since it would break lots of traffic.
Note that increasing this value will increase the memory used on every relevant
push that Git does over HTTP or HTTPS, since the entire buffer is allocated
regardless of whether or not it is all used. Thus, it’s best to leave it at the
default unless you are sure you need a different value.