Downside is more work, but the extra cash is nice!

that's the down side of max debt.. 

The up-front costs are much lower than the other options, you don't pay any interest until you actually use the money, and only pay interest on the money you do use.The downside is that the interest rate is higher, usually floats, and is amortized over a shorter period.

It has ramifications and downsides. 

There is definitely a crowd that "sleeps better" knowing their properties are paid off or have low leverage.I think there is a happy place in between - one that lets you take advantage of the growth leverage affords, but has enough equity and cash flow to protect against downside risks that recession brings.    

That land can't be developed anyway so I doubt there's a downside to doing that. 

Also, if you are time rich and money poor, you can build a lot of sweat equity by doing the management or working on your directly owned properties and generate a higher return The downside is that of course all of that takes work and effort.

It seems like a very easy way to get into investing, so I was wondering what the common pitfalls and downsides to using a master lease option all the time would be.

I'm not arguing, just curious . . . do you see a specific downside to it?

The downside with these approaches is you do not extract your capital from the property upfront.