In general you do want to see a spread between your cap rate and interest rate. However, there are interest only loan products that can allow a property to cash flow for several years because the debt service doesn't include pay down of the principal.
In multifamily, many standard or agency lenders aren't going to lend on a cashflow negative property. Look up Debt Service Coverage Ratio. They usually have specific criteria for DSCR ratios which means that the property has to generate enough cashflow to cover the loan.
This article covers cap rate to interest rate spread:
https://www.qreadvisors.com/re...
In single family, the way properties are valued is different (comps). You may come out of pocket $10K per year on a rental property's mortgage but gain $25K through appreciation in certain markets (i.e. California). Personally, if an apartment complex doesn't cash flow, you probably want to look the other way, because that's how apartment complexes are valued--they are valued based on cash flow and rents.
However, there are people who take advantage of a cashflow neutral or negative property (i.e. high vacancy, poor management, down units) that will be purchased as cashflow negative and quickly transitioned to cashflow positive. Typically they will use bridge debt or similar until they can achieve a DSCR high enough to transition to agency debt.
The cap rate of a property IS important, but it's important for new investors not to invest solely based on cap rate. If you are purchasing a property at an 7 Cap in a market where all properties of a similar vintage trade at a 5 Cap, that should cause concern--not be a green light to invest because it's a "better deal."
Similarly, investing in a random sub-market where properties sell for an 8 Cap instead of a major market where properties trade at a 5 Cap doesn't mean your total return over 10 years will be better if the 8 Cap is in a market with flat or negative rents and the 5 Cap is in a market with 3-5% annual rent growth.
A Cap Rate is generally used as just another indicator of market sentiment on a particular property's income stream. In some markets, properties will trade at higher Cap Rates because the expected growth rate of rents is very low. In other markets, properties will trade at low cap rates because the expected growth rate of rents is very high.
Additionally, interest rates DO affect cap rates--to an extent. If interest rates were currently at 6%, it would be highly unlikely to see properties sell at a 4.5 Cap. However, interest rates have gone down significantly (as low as 2.7%) which means the spread between your interest rate and cap rate can be as high as 1.8% on a 4.5 cap.
See Brian Burke's article below for more nuances regarding price at sale:
https://www.biggerpockets.com/...