What are the advantages and disadvantages of I2C?

Advantages:

I2C's greatest strength is its minimal pin count — only two wires (SDA, SCL) regardless of how many devices are connected. A bus with 20 sensors, EEPROMs, and port expanders still uses just two MCU pins. This is invaluable in pin-constrained designs. The built-in addressing scheme (7-bit or 10-bit addresses embedded in each transaction) eliminates the need for dedicated select lines. Multi-master support with non-destructive arbitration allows complex topologies where multiple MCUs share the same peripherals. ACK/NACK at the byte level provides immediate feedback that a device is present and received the data. Clock stretching gives slow slaves a way to throttle the master without data loss.

Disadvantages:

I2C is half-duplex — a single data line means data flows in only one direction at a time. Maximum speed is limited: standard mode is 100 kHz, fast mode is 400 kHz, and fast mode plus is 1 MHz. Even at 1 MHz, I2C is 10-50x slower than SPI. The pull-up resistors and bus capacitance create an asymmetric rise time that limits speed and bus length. The I2C specification caps bus capacitance at 400 pF for standard/fast mode, which limits practical cable length to 1-3 meters depending on speed. A single misbehaving slave — one that holds SDA or SCL low — can lock up the entire bus, and recovery requires the 9-clock-pulse procedure. The addressing overhead (device address + register address + ACK for each byte) reduces effective throughput for small transfers. Finally, electrical noise on SDA can be misinterpreted as ACK, causing false positive acknowledgments — there is no CRC in base I2C.