Embedding xls in ppt sounds like a good idea. At the moment, though, the only two use cases I can think of are: (1) Inadvertently generating Powerpoints that are far too large, or (2) Making it easier for attackers to take over your system.
OLE/COM allowed me to use some flash animations as part of a powerpoint about a decade ago... Also, being able to chart live graphs from excel isn't a bad thing. All of that said, I don't regularly use PowerPoint, and MS has at least been forthcoming with the issue (far better than in the past)
Interestingly, the use of Flash exploits eventually became common enough (it was used to hack RSA for example I think) that Adobe go out of the way to detect older versions of Office and throw up a warning message.
Yeah, I worked in a company that had a legitimate reason to be able to save state (the local file system) from flash before storage solutions inside of flash (around 4 to 6 iirc) a COM injection bug was used to access the filesystem... after I saw what could be done (COM injection), I promptly disabled flash on my own computers.
