TCP Sockets send buffer size efficiency

When working with WinSock or POSIX TCP sockets (in C/C++, so no extra Java/Python/etc. wrapping), is there any efficiency pro/cons to building up a larger buffer (e.g. say upto 4KB) in user space then making as few calls to send as possible to send that buffer vs making multiple smaller calls directly with the bits of data (say 1-1000 bytes), other the the fact that for non-blocking/asynchronous sockets the single buffer is potentially easier for me to manage.

I know with recv small buffers are not recommended, but I couldn't find anything for sending.

e.g. does each send call on common platforms go to into kernel mode? Could a 1 byte send actually result in a 1 byte packet being transmitted under normal conditions?