Thoughts on Using a Float For 2nd or 3rd Joint Coats

I've used a 6" knife for the first coat on tapered joints. I saw someone using a float on YouTube for doing subsequent coats. I used a float for plastering the cement render on the outside of my workshop and it turned out fine, but what if any are the disadvantages of using it for joints on plaster rather than using a wide knife?
 
I've used a 6" knife for the first coat on tapered joints. I saw someone using a float on YouTube for doing subsequent coats. I used a float for plastering the cement render on the outside of my workshop and it turned out fine, but what if any are the disadvantages of using it for joints on plaster rather than using a wide knife?

painters use knives and plasterers use trowels...
 
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