I know this thread has been dormant for a while, but I am in the process of planning to rehab a historic property myself, and would like to hear more on the topic.

After, @andrew crowley 's comments, however, I think the smarter play may be to use the margin for investing and transfer some cash from the checking account that's sitting dormant earning no interest into the margin account to reduce the interest payments on the LOC.  

After that point it then lies dormant inside the property and waits your passing and the step up in basis.  

The bugs can lay dormant for a long time (hidden in the carpet/baseboards), so you may have had an issue already and then the tenant moves in and months later starts getting bit when the bugs become hungry again. 

It creates activity on the account and prevents it from going dormant.

I closed a bunch of dormant credit cards a few years ago and pretty much only use one credit card, which I pay off the balance every month.

If the crawl dries to a point of being dusty for long periods of time the mold may go "dormant" where new spore production is concerned. 

This board has been dormant for awhile.

And if you do flipping, you might want to make the LLC dormant (or look into Series-LLC if that's an option for you).

Is it possible that the cheap-o cleaning got some dormant dog smell wet and all it really needs is to finish drying out again?