I don' know what down side you may run into house hacking to be honest.

If you choose to make Roth contributions, your qualified distributions are tax-free.On the downside, there are prohibited transaction rules that prevent you from using the retirement funds in your own interest before taking distributions.

I could imagine houses/scenaros where they are needed, but most homes its mostly downside

Just realize one should consider the risk being taken on as well as the downside. 

The downside to the smaller properties is many times they are not well managed and books are spotty.

But the downside to that is that you have WAY more invested in the property.From a return on investment perspective, you lose that way.  

Every town in RI is mandated by the state to have a certain # of affordable housing units, and nearly every town consistently fails to meet that mandate, so they are very accommodating of projects that help them meet that goal.The downside is, your property will be worth less for a few decades while that affordable housing limitation is in place (less income = less value), but if that's the difference between being able to build and not being able to build, that could still cause you to lean to build anyway.

The big downside to this is that banks to pay for things until they are installed.

i live in LA and during the recession just about everyone i know negotiated their rents down. it happens. just make sure your numbers work and that you have some downside protection, especially if you think we are at or nearing the top. a lot of people who bought between 2010 and now have no complaints about riding the market up and are happy to share their success stories, but a lot of people who were destroyed by the crash may not even be on bp. if you are buying on thinner margins, make sure your numbers are sound, you have some protection and enough reserves to weather a storm. 

There are ways to do things like cost segregation studies to accelerate some depreciation but there are also downsides to that approach that you need to understand, and in any case you're not going to write off your total money spent on the property in year one no matter what you do - it makes no difference from a tax perspective if you pay cash or borrow money, other than the interest paid.