I work toward a savings goals for the year (set in dollars) both for investing and for other purposes/projects; when combined with other budgeted expense it leaves me with a leftover amount as discretionary. That discretionary amount remains relatively constant from month to month.
That means that if I reducing savings this month to buy something I will be boring from future months (DEBT) if I still want to meet my savings goal or I neck down on my discretionary spending for however many months to save and buy it outright. I prefer to save and buy rather than go into debt, even if it is to myself in regards to a self imposed goal. Actually, I've got a few things that I know I am going to buy that I am saving towards right now.
I would also be able to justify way too much by saying I will buy this at some point so why not now and I would be in too deep a hole to climb out of by the end of the year with just the discretionary funds. And if "will buy" is the justification for going into debt to myself (as I call it) where do you draw the line; well if I just spend 50 bucks a month less for the rest of the year I can afford that compound miter saw that I am going to buy today, well if just draw down my savings/sell so much of my taxable I investments I can do that bathroom remodel we are going to do now, well if I just put it on the credit card I have 6 months 0% interest, well the interest rate is only 0.9. . .You may be different, but for me I like to stay ahead of the spending rather than playing catch up.
Of course there are unexpected things that throw the discretionary into disarray, such as an unexpected health issue/home repair/auto repair, which needs to be addressed at that time and I just have to deal with it.
In the past I have bought a few things that I was definitely going to buy early for various reasons (it went on sale, it will be easier to install before winter sets in, I will get more use out of it this season if I buy it now) and many times the budgetary changes after the fact made me resent the purchase (even though I still would have bought it); in contrast I rarely regret (at least as much) a purchase I saved up for and have no obligations to afterwards.