Does the STOP condition have any meaning on a single master I2C system?
The STOP is an indication to the slave device that communications are complete. It's ingrained in the protocol and spec-compliant slave devices expect to see it, so you simply can't wish it away.

For instance, if you're doing a page-write to a 24AA04 serial EEPROM (up to 16 bytes of data), the EEPROM will stop buffering data and start writing to flash upon receipt of the STOP from the master. You're not obligated to send a full page, so you need the STOP as a clear indication that there are no more bytes coming. (Some EEPROMs will throw away pending transactions if a STOP is not received at an expected/appropriate time, which can lead to some head-scratching debugging problems.)

Some devices also use the STOP to enter a reduced-power-consumption mode, drawing less power until the next START wakes them up.