I start any file based programs with strict and warnings. But I rarely -Mstrict with -e. Often that means that when a -e program begins to grow to the point that my shell's (bash or cmd.exe depending on platform) readline is more cumbersome than moving the code into a file and bouncing to a shell to execute (or keybinding to execute for editors that handle it well) I move it to a file, usualy adding strict and warnings before I even copy the code from the command line, and then forgetting before the first time I run the file that I still need a few my's sprinkled around.

I'm fairly good at judging before hand what will be a one off with maybe an edit or two and a program that will require editing and debugging, but ever couple of months I'm not so lucky.