When you build enough capital/assets/net worth to afford a reasonable monthly cushion you can see if the lifestyle of a full time investor is something you’d want to pursue.  

That 4% mortgage is a real asset.

For long term, the main benefit is having someone else pay off the mortgage on an asset while you collect cash flow.

Reason is a Heloc generally carries a higher rate on a shorter term and "Can Never" be used as an "Asset, or for PITI reserves" which are both required when you buy an investment property. 

Never invest in Longterm assets with short term debt.  

Of course, the smart ones will have agreements stating they are involved in due diligence, marketing, asset management, etc.  

If they are not good at property and asset management your "investment" could become a money pit with vacancy and repair expenses. 

These loans are short-term, asset-based, and designed for situations like yours.

Every bank at that time had way too many non-performing assets on its books.

@Cristal Ochoa @Leiah DotlichI will preface this with the fact that I have a legal background, specifically with estate planning and asset protection.