Drano, getting into some heavy video transcoding, audio transcoding or something like using Photoshop for doing commercial graphics, using AutoCAD designing HVAC-R/plumbing, engineering blueprints etc... are some of the things that can and will happen to heavily tax a computer's system Ram....
Even more so in the old days before Windows 7...( WinXP, Win98, Win95, Win for WGs 3.0/3.11 etc ) where we used batch files and used the PAE, etc...
TC