They're mainly used for multiple amp setups. For example: you wanna run one power wire from the battery to your trunk then use a distrubition block to split that one power wire into 2,3,4,ect. wires to go to however many amps you have.
I'm not positive on this, but I'm pretty sure that a distribution block can be used for ONLY power or ONLY ground unless other wise noted, not together. The one you are looking at seems like it has 2 inputs for 2 wires (ground OR power) to hook up to 8 different amps..
Like he said you usually hook your large 12+ cable from the battery to the block near amps, then run off it to your multiple amps. That short connecting wire can be smaller gauge...you need larger size the longer distance you go (like battery to trunk). Then you usually ground each amp to the car with a short wire. Then ground your battery to the body good as the factory wire may be too small. Some run a ground back to battery too and do other stuff.
Yes but, you should check your HU for draw it can supply for the remote. I've run 3 amps and a crossover but was told some newer HUs you should use a relay so I don't know how many amps you can run. My HU is maybe 10yr old or something. I would just hook it up but this guy was a dealer he said and pretty serious about it when I questioned the need for a relay.
relay are needed when running 3 + amps. Most amps require very little rem voltage. Its fine to run 2-3 amps off the stock HU rem. Hook em up stock, if it gives you problems look into a relay. I figured if dude was having a hard time with D-blocks, now not the time to be confusing him with relays.