Commonly understood in the field^ is that 60,000 examples is the sweet spot for training and validation data, 50k for training 10k for test/validation. This is largely because the MNIST set is exactly that size and is so commonly used successfully. Get very high accuracy and reduces instances of overfitting. That said you can do a lot with a relatively little set. This 2012 paper puts the range between 80-570 samples…
I don't understand how this could be true. Shouldn't the sweet spot be a function of the dimensionality of the data?