MITM
These days having a chart plotter is so much better with what you can view, eg your trail of where you are and where you have been, in case its dark or foggy and you then can come home following the trail you came out on. Thus, a great navigation tool.
The CP will have a modern map of the area which may show reefs and interest for fishing/prospecting... new CP will have bathymetric mapping as well for more depth contours, very useful when looking for new ground.
And of course you can mark and plot all your areas of interest and your own spot x's for future reference.
If you are only fishing in close and not over 150m then a standard 200Khz model of sounder/fish finder will suffice with standard transducer, but if you are a tweaker and want to examine the fish/bait and contacts mid water and good definition of structure on the bottom, then ask for the narrow beam high performance transducer to match the sounder/FF.
Also with the CP... the best bit is cruising over and area and seeing great fish sign and creating a waypoint or mark and then drifting back over that or the rock you have found.
Very well worth the extra funds mate.
"The sea, once it casts its spell, holds one in its net of wonder forever." - Jacques Cousteau