As far as memory goes, every show I listen to says android was intended to use all memory available. One even suggested to not even pay attention to "used memory". Idk, but seems my device runs a lot smoother having at least
75-125 mb free.
Sent from my MS-5 Glitched up fascinate
In computers in general, free RAM is in effect wasted RAM, but only to a point. Here's a good realistic example: the settings app takes on average 20-30mb of RAM. If you only have 4mb free, it has to kill an application or two or three before it has enough space to load into RAM and launch. That's why computers, and by extension android, uses low memory killers. When you get below a certain amount free, it will kill the inactive/old applications, so that you then have room to launch big ones when you want. Also with android in particular, certain things like to live in RAM all the time, such as your launcher, mms, and some oddly coded apps (I'm looking at you, drop box and Google maps) or things like Google talk and email clients, that will be recieving info a lot. That is why ram management applications don't work well on android, because they keep killing the same apps, that then restart themselves again, only to be killed later. I know that was a little more info than you were looking for, but useful nonetheless