RS232 needs relatively high voltages; plus and minus twelve volts, in general. Thus, you need RS232/line drivers to convert between them and the TTL/CMOS voltages required by your UART.
RS232 is popular for connecting to PCs.
RS232 has a limit of 256,000bps over a couple of feet. The max. speed drops the futhur you go. RS232 is current limited if the correct driver chip is used.
RS232C is +-12V signals RS232D uses +5V/0V signals and is was standard on laptops a few years ago.
RS232 is the same as the ITU (CCITT) V24 standard as far as signals go.
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