Benefits of DAC & Transport vs. CD player

I own or have owned separate dac's, transports and CDP's.
Some suggest that separates sound better than a single CDP, and in some cases that is true. I have found that it all depends on the individual quality of each manufacturer product.
To make a blanket statement that is a generalization would be a mistake.
A single player does take up less space with one less interconnects, and visa-versa.

I agree with Lak's comments, you can't generalize because it all depends on what combo you are comparing with what cd player. Right now I use an Acurus ACD-11 as my transport as a lot of time and expense was put into that unit's air dampening system to reduce the effects of vibration and in turn jitter. The technology on the electronics side is now a little dated and so I run it with a DAC to for instance decode HDCD recordings. It is likely that if I upgraded to a current single CD player such as the Cambridge Audio 840c I would hear a sonic improvement but it would come at a monetary cost.

Having just upgraded to separates, I would say the deciding factor for me was flexibility and performance. I needed to get a separate dac anyway for me to send my digital music to anyway. If I was going to get a separate dac I then thought about using my current cdp as a transport only. But I did not like the idea of "wasting" the other features of my cdp. I figured I could sell my cdp and get a transport only device with better performance. I also preferred to get a dac and transport combo from the same manufacturer. I was also able to get the newest version of a dac from Esoteric that has the new AKM 32 bit dacs which I wanted to try. Anyway, for me separates made sense.

For some people the argument for a separate DAC is that, once you have more than one digital source feeding your main system, it makes more sense to buy the best quality DAC you can afford and use it for all the sources rather than spread the same money over multiple DAC's inside the source boxes.

I don't think there is a definitive answer to the original question. From experience though, separates require extensive experimentation with the digital connection to sound their best. This plus an additional PC can add considerable expense to separates over a CDP.