Andrew Robson
Shohin
Cakes, Slow release pellets and such offer you little control of the contents...
Liquid fertilizer can be mixed to precision and applied as you please.
Actually most bonsai professionals would disagree with you. Assuming we are using volcanic soils (pumice, lava, akadama) the benefits of cakes is that once you want to stop fertilizing, you simply take the cake off, like after black Pine decandling. Furthermore, you can really fine tune your fertilizing precisely to the trees needs, which is really what bonsai is about. Therefore cakes offer you the most control of all fertilizers.
Unless you want to mix a different batch of liquid fertilizer for every tree you fertilize, you won't be fertilizing your trees correctly with a blanket dosage for all your trees... Also, have you done soil analysis to test which liquids hold in the soil? And, are you using an organic substrate in your soil? Organic material will hold liquid fertilizer for much longer, and certain liquid fertilizers stay in the pot longer regardless of substrate, like fish. Dyna Grow gets used by the plant and washed out quite rapidly. There are much more uncontrollable variables with liquid fertilizer.
Going back to volcanic soils, one of the many reasons professionals and serious hobbyists like them so much is because you can really pinpoint your fertilizing. Want to stop fertilizing black Pine after decandling? Simply take off the cake, water your tree, and most of the fertilizer will be gone. This is how we do bonsai, we are extremely picky about most things and the more we can accurately pinpoint things like fertilizing, the better the results.