I know of no way to get 4% guaranteed return on my money, and do not wish to go through the trouble of attempting to secure a really great rate on a loan. Also, I far prefer the flexibility of having greater free cash flow each month. To each his own.
Edited to add: When using a loan, it’s far easier to spend more than you have. Paying cash forces one to stay in budget, and requires the discipline of saving up front- which is never a bad thing IMO.