Really depends. If you take out the mortgage equation, all that money saved can be then poured into the next multifamily. If you have a vacant unit or two and you have a mortgage, then you will still be paying the mortgage with no money coming in. I only have mortgages on my really large units. Larger units, larger problems. I am not a fan of borrowing money and growing slow. If you have cash, cash is always the better way. When the housing market crashed in 2007 - 2009, many people with cash were buying up the properties for cash and holding them w/o a mortgage. Now, if you can get a mortgage rate between 2% - 3.5%, sure it makes sense to do so. However, for investments and non-owner occupied homes, the rates are usually 5%+. In addition, the closing fees are pricey. This is why I prefer to buy with the funds I receive from the rents on my units and then buy other units. Some are rehabs, some are not. I am a hawk on expenses, so it is important to keep them in line or when the sh!t hits the fan, you will be upstream without a paddle.
Just remember, leverage is good and bad. It is good if you can control costs and have enough leeway in good and bad times. In bad times, when the vacancies and evictions go up, and you have 10+ mortgages to pay, chances are money is going to be tight. If you are just starting out, trust when I say, start with one, then two, and so on. Slow and steady. You will undoubtedly make mistakes, we all do. It's better to make mistakes on small 2 or 3 family buildings than on 10+ apt. complexes. I only had mortgages on my complexes, because I wanted to unlock those funds to buy other buildings. Example. I purchased a 15 unit two years ago for 500k for cash, it's appraised value was 640k. I had to put 50k into the complex, and I then received an 80/20 mortgage for 445k on the upgraded value. I then took that 445k and purchased three other buildings. One for 40k, one for 215k, and one for 200k. I rehabbed the 40k building across from a major area for 250k, and it's appraisal is over a million dollars. The second one needed about 40k, and it's new appraisal is 300k. The third needed about 50k, and it's worth now about 450k.
In the above mentioned real life example, mortgaging a complex is worth it. However, I am tempted to sell the complex as it's a major headache. The later three have no mortgage, but I have the option in drawing a credit line on them; should I need. Mortgaging a building under 250k doesn't make much sense if you have the funds to pay cash and hold. Yes, you can go over to Bigger Pockets and they say mortgaging and leverage is the best. They are making 200 a unit. Wow. Cannot live off that. However, if you do not mortgage and go cash, you are then making 600 a unit (or more). It really depends on what your tolerance is and how much money is backing you.