If there is not enough current, your circuit may not be able to do the work it was designed to do. Logic circuits may not function reliably, displays may be dim, motors may stall. On the other hand, if there is too much current, things will heat up and components may be damaged. In extreme cases there may even be smoke or flames.
Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.