See, I don't see predicting your spending as a fool's errand at all, not if you have tracked your past spending to see what you've actually spent in the past. I see it as a self-imposed limit on some purchases. Like a lot of things, it's all about choices and priorities. I use YNAB, and do some of both.
How I budget varies greatly on what my goals are at a given time. Before, when my goal was just "save what I can", I didn't make a budget. I just checked my accounts at the end of each month and made sure they had grown by a target amount (let's say $1k for checking/savings). I'd come to that target amount by taking my income and subtracting all bills and "reasonable" spending. If I didn't see my bank account go up by $1k, then that meant I overspent that month, and would check my spending a little more the next month. Once a year a large bill would have to be paid, so I knew that that month I would not see that $1k target. If I was saving for a big vacation, I'd decide how much I needed to add to the target, so might make it $1.2k/month. I'm single, it worked great, for my goals at the time.
Now, I have a few large, and separate, savings goals. I want to build a house on my property, help my son with college, and pay for a newer car. During this time, I still want to fund some vacations, my quilting habit, and make sure I'm saving for all the "unpredictable" things like home maintenance, car repair/maint/tires, etc. So, until those large three goals are achieved, I need to have a better handle on where everything I spend is going, and make sure I'm happy with my saving rates on all my goals.
Anything that has an annual fee has a category (Costco, PO box, photography club, etc). I know what the annual fee is (or should be), so I put some money in each category every month.
I know I will save a minimum of $x amount each month for my son's college, the house, and the car, so those each have a line.
Every bill gets a line.
Every non-monthly but "known" expense gets a line (property taxes and similar).
My hobbies get a line so that I can add a little money toward them when I work some OT, but I keep spending on those in check otherwise.
Groceries, fuel, eating out, etc get a line. I can "predict" what I spend each month here, but it's mostly there to keep that spending under control. Some months we don't go out to eat at all, so that just builds up and maybe we'll go for a nicer meal once instead of blowing it all on fast food. Groceries could get ridiculous if I didn't set a "predicted" amount each month to aim to stay under. I let the fuel line build up some funds, knowing I don't spend it all every month, but a road trip, or more trips to the property, will cost more than a regular month. The leftovers just build up a "slush fund".
My car repair line gets larger as a car gets older or I know I'm going to be due for tires soon. I save some every month to build the "slush fund" so that regular maintenance is covered, but also a little toward tires, etc, for future expenses.
"Fun Money" gets a line so that I can purchase whatever without guilt that it's cutting into my savings. Some months I use it all, some months I just let it build. Makes dropping a few hundred on show tickets easier, because I know I've already set that money aside just for the fun, frivolous stuff.
Each savings goal gets a line. I really like to see these categories grow. When I work OT, I drop a little extra into several categories (fun, car or home maintenance, groceries, etc) so that I feel like I get a little instant gratification from the extra income, but then I dump the rest into these categories and it feels really good.
Once my son is out of college, my new house is built, and the car is covered, I'll probably go back to my old ways of just making a target each month. Tracking the spending and creating specific goals has made me very aware of my spending, and cut out a lot of "bad habits". I'm naturally frugal, so my spending was never really out of hand, but it wasn't helpful toward what I really wanted.
TL;DR, budget should be based on your goals and priorities, saving for those "emergencies" so they don't catch you off guard, and allowing you to save money where you don't care so much, so you can put more money where you do care.