A bashed patch compiles all the changes made to the game, or an object, by mods, so that the one you want to win does. In other words, if two mods change a sword, the bashed patch, via load order, can determine which mod wins and makes the change. It can also make sure your leveled lists work so loot from one mod will show up as it is supposed to in a container.
In other words, if you have more than one mod, and especially if you have a UOP, then you need a bashed patch.
What to put in a bashed patch is the tricky part. The basic stuff that is already checked is a good start. But, if a mod is not working right in your mix, then some tweaking is needed to something.