I tend to refresh my map documents every 3 days or so. By that, I mean I drag all my layers into a blank mxd, and save that as my new working document.
After a round of analysis and editing (the length of the round varies), the current mxd seems to get “tired”. ArcMap takes a few seconds longer to respond if I make a change, open a tool or do anything. Closing that mxd and opening a different one results in ArcMap functioning as expected; try opening that first mxd again, and it’s back to slowness and frustration.
This tends to happen particularly with mxds containing CAD drawings, or ones I’ve used to perform a lot of edits in. I’m not sure why it happens, all I know is that if ArcMap starts “getting slow”, I open a blank mxd and carry on. I don’t fight it, I just accept it for what it is.
Now that ArcGIS Pro is doing rounds, I’m hoping that this won’t be an issue anymore.
This doesn’t bother me as much as it did before, as I do most of my work/processing through Python now anyway. If I really need to, I open ArcCatalog to look at something.
The problem gets a bit more serious when geoprocessing tools start failing randomly, and you spend three hours checking your inputs, modifying parameters and pulling your hair out before you remember to open a blank document, run the same tool in there and get the results you were expecting.