[flyingfrizzle]

It is best to start with the run from the fuse block if you have one. It becomes a main point of distribution. Secondary fuses on the switch panel are not needed if you fuse each switch from the main panel separately. But if done like in the diagram they show a common (+) on a 25 amp fuse feeding all 6 secondary fuses that are being switched to field devices. You may have a radio that needs a 3 amp fuse and having separate secondary fuses before the switch gives you the chance to rate each power source at the correct amp limit. The 25 amp main fuse will catch a dead short but then you may not catch a problem at 10 amps on a 5 amp device. Also you don't want one fuse blowing out killing power to all other 5 items on the switches that are fine if only one circuit has an issue.
So you say what do I need the 25 amp for if the switch panel already has fuses? The main 25 amp in the drawing is protecting the wire feeding the secondary fuse block. If you use #4 awg from your battery and have a 60 amp fuse with in 18" of the battery (+) that will protect the feed to the fuse block but you still need to protect the smaller wire to the sw panel. A #12 will melt or burn before the 60 amp would blow. In the example drawing it shows #10 from the battery source, and if you feed the sw panel with same size #10 also and don't go smaller with #12 as shown then you would not need to fuse separately prior to the sw panel. So a 30 amp fuse on the #10 protects it the whole way. If you drop wire size like they did then you need to fuse the smaller size wire with the correct fuse.
If possible you always want a fuse with in 18" of a battery terminal (+) and then fusing where you distribute the main down to smaller wires. Now if you had a large enough fuse distribution block you could put all your fuses there and feed each switch separately off the correct fuse for each device and not need the second ones at the switches. Fused switch panels are more for use where you are not near the main fuse block. That way you can run one (+) wire to it then distribute. But if the block and sw panel are a few feet apart you could run 6 feeds to the switches individually and keep all your fuses in the one block and out of the salt water on the console face.
It is also important to make sure if you use two separate fuses on the same feed such as coming off the sw panel make sure the first fuse that splits to the other fuses is large enough to feed them all with a 20% factor added in. Say like in the example with 6 feeds from the sw panel each switch has a load of 5 amps. 6x5=30 amps total. The 25 amp fuse may blow and not hold the switched devices. If they were 2 amps each 6x2=12 amps now the 25 amp in the drawing will work and you have enough overage that the smaller fuse on the sw panel blows first. If you did end up with 30 amps total draw on the switch panel you would want to up the main fuse to a 35-40 amp. But if you up the fuse feeding the secondary fuses make sure the wire between the two is rated to carry what you are fusing it for. A #12 will not carry 40 amps and you would need #8 instead.
As per the drawing the entire system is being fed with #10 which is not large enough either in my opinion. If you use each item on the boat separate and never have more than 2-3 devices on at the time you may be good. Soon as you try to run a lot of stuff say at night such as lights with the radio going and several other devices together you will kill the main fuse feeding the whole system if not sized correctly. Worse off if you have #10 feeding the system and no fuse on the battery you will melt down the main feed from it. To be safe add up all your total load together and make sure you have enough wire size to feed it all. The #10 in the drawing used as an example seems small to me when feeding all the devices shown. Now with new led lights that don't draw much current you may be ok but again add up what the manufacture show as the max amps on everything in the boat and then design you system with larger capacity so you have some cushion. You may want to add stuff to it latter also.