Another advantage to side dressing every other row - 8 outlets on 16 rows - is that you do not have any outlets with double or half rate nozzles. All 8 coulters etc are the same rate. But uniform flow division between those 8 is still important.

I have seen very wide side dress units poorly plumbed and produce real green corn in the center and real yellow corn out on the ends.  This is not a problem with the 60" system but a plumbing problem that can happen with dry, liquid or anhydrous systems.

Each row unit on 60" side dress units does need to handle twice the rate that it would on 30". I feel it is even more important on 60" to  make sure the fertilizer is down below the soil surface and covered/slot closed. 

Jim at Dawn