I'm seeing a lot of growth in my area, Vancouver Wa., just north of Portland and much of the time I see people building/remodeling their operations with little to no experience. I see too in too many areas overall where the hired help is not exactly in their field, taking much longer then what an operation in that field could achieve. I think most get into it to save money, or at least they think they are saving money, but it's not necessarily the case.
I can start on the simple side here, where every day you are delayed for opening, is one day's of profits gone, also every day you are paying for lease of the place and it's not operational is also money out the window. It's one of the reasons I rarely deal with selling used equipment, for an espresso machine down for a day, or refrigerator, or any other key component is profit's lost, so that so called deal you got wasn't such a good deal after all.
The pro's if they are seasoned know how to get the best supplies at the best rates, hopefully handed down to you in the process, which in turn makes up for their labor costs. Since they have been doing this for a while, they are going to automatically know how much of what to buy, what to assemble and how, also carrying their own compliment of specialized tools and equipment. You can only Youtube or Google up so much along how to do things, it still takes practical real world experience to perform any given task with fineness. The biggest mistake made by the DIYer is not planning into it every iota of detail from start to finish before commencing with the build. It's always starting at some random spot, trial and error, sitting back scratching heads along how to approach the next obstacle and moving forward, hardly a smooth process.
I see others that are hiring contractors that are either out of their field or are milking the clock because they are used to residential construction so figure these people are doing some fancy coffee shop, they have deep pockets, might as well take advantage of it. I see this happen even with the biggest players in the industry, and I am appalled seeing yet another 2x4, dry-walled up customer work area. Drywall and 2x4's are for walls, not commercial cabinetry... The new to the industry shop owner may not know all of the technicalities involved so assume what their contractor is saying is the norm, but it's not necessarily so.
I see advantages though through DYIers filling in the gaps, such as painting base boards, prepping the areas, cleaning up, odd things as well that would slow down the progress of your hired help too. I do see some that are smart enough to section out the duties and sub contractors, essentially taking over the roll of a contractor, and some with plenty of personal background that are more then capable, but that's rare.
I will say though, if your research is extensive, you have practiced the techniques for construction, know what part and sections you can handle and what to outsource, DIY can save money and time, but only if you are realistic. It's not like painting a fence, start on one end and end up on the other, there is a myriad of things that intertwine.