I think it depends on the harbour you are entering. With a harbour like Poole where you have deep, wide, well defined and stable channels, it is relatively easy to use your plotter to navigate the channels.
But with a harbour like Xchurch where you have very shallow, changable and very narrow channels you have very little margin for error using your plotter alone, and a very short reaction time to make direction changes without hitting the mud banks. In this case, the plotter is best used as guide only to allow you to predict where the next turns are, and where to look for the next bouys.
The bottom line for Xchurch is that you cannot reply on the plotter. You need to use the bouys to navigate, which means you need a powerful torch or spot light to find them.
That's my view, anyway.
Bob F.