for rom install, i wipe data (which is same as wipe data/factory reset in CWM); wipe cache; wipe boot (which is same as format boot in CWM); and wipe system (which is same as format system in CWM). here is the explanation RZ gave in his thread about the different wipe options:
Wipe All: This will wipe out EVERYTHING on your phone except for recovery. Only do this if you have a backup, SBF, or rom ready to go either in update.zip or rom.tgz format. This is not the same as a factory reset. A factory reset only wipes out data partition (leaving system, cache, android kernel, etc)
Wipe System: Wipes the system partition, where the guts of the system live. This and a kernel is all you need to boot android. Themes get applied to system, all the contents of a ROM live in system. This contains android framework, libraries, binaries and all apps that come with the ROM. Apps you download are put into the data partition. See why wiping data is considered a factory reset?
Wipe data: Wipes the data partition. This will reset all user data, downloaded apps and settings. This will reset your phone to the state it was when you first installed your ROM, or received your last over-the-air update.
Wipe boot: this is where the kernel that boots android and you know and love lives. If you are having trouble with your boot partition, wipe it and install your kernel again. But be aware, update.zip kernels in koush's anykernel format will not work since they are only half of the puzzle. anykernel packages only supply the kernel itself. The boot.img (image of the boot partition) contains the kernel itself, and the initial ramdisk (image of the entire filesystem, to include startup scripts that define what shortcut keys are what, what the initial clock settings, etc are). without a initial filesystem for the kernel to boot, your phone will be useless. This is why I have provided a raw kernel image flash utility in the install menu. It is in the raw format that I distribute my kernels. Developers can also simply put a full boot.img in update.zip as well, this is how ROM's default kernels are installed.
Wipe Cache: No real useful data lives here, recovery information and log files, but not much else. My recovery custom color data will be here, so if you wipe cache you will have to set your color again (note, I do not have the color feature working yet).
Wipe Misc: It's a mystery. Nobody knows what it's used for, wipe it all you want or don't wipe it, it doesn't matter. I only included it for the sake of being complete.
Wipe Battery Stats: over time, your phone learns the battery history. It stores this information in a binary file /data/system/batterystats.bin When swapping ROM's, it's a good idea to not confuse the system with old statistics from different kernels for example. One of the reasons everyone says to wipe (data) when switching ROMs.
Wipe Dalvik-Cache: The dalvik cache is a place where Dalvik (the modified java virtual machine that runs Android) keeps its local versions of the apps you run. If you ever look in /data/dalvik-cache you will a bunch of *dex files. These are basically as far as I can tell no different from their compressed forms in the individual APK's (for apps) or JAR's (for framerwork) except that they are ready to be used and I assume their presence is strictly for speeding up day to day operations of loading and unloading apps. Since the actual java code rarely changes (unless you are xeudoxus or maybe myself... hehe) the system keeps a cache of them in dalvik-cache. When you apply an ultra intense theme that changes any java code (actually it changes the dalvik bytecode that the java is converted to in order for Dalvik to interpret it) you will want to wipe the whole dalvik cache or at least delete the cache files that you have made changes to its originitaing app. Note, when you wipe the dalvik cache, your next boot will take a long time, this is because (I assume) that it is extracting the code from each app again and creating a new dalvik cache. Phew.. that was a long one.
Hmm... and doing "reboot recovery" from adb does the same thing. Does the standard boot re-flash the recovery, or something?