this has been covered a LOT .... but for yucks, I will add my most recent thinking (I am only about 1.5 years into this also). First of all .... most of the knives I make are longer kitchen knives .... 6 inches or more .... so the thought of really effectively getting more than one knife out of a single belt is .... no longer in my thoughts. From what I have been seeing, it is really about performance - and performance goes DOWN the second a belt touches steel. Second, it has become really apparent to me recently that when doing a full flat grind, it is MUCH easier to create that long blade-width flat with a new sharp belt than an older duller belt. third, sharper (newer) belts definitely do not heat up the metal as quickly.
Putting all that together, today what I do is: use an old 60 grit belt (hopefully only used once) to grind in the 45 bevel as I am starting the grind, and to take it down maybe 1/2" or so down the blade. then I shift to a new belt, and hopefully can then complete the grind for the entire blade with that belt (this allows for really establishing that flat, and hopefully keeping heating down to a minimum). That now-used 60 grit belt now becomes the one I use to establish the 45's for the next blade, etc, etc. I have gotten to the point where I am using that 60 grit belt to take the edge down to 0.005- 0.008 .... BUT am making sure my flat grind is FLAT (or as much as I can make it). THEN I shift to a 120 grit .... and from then on it is really surface finish refinement, NOT actually removing much metal. the 120's thus last a while ... several knives (until either they are not easily removing the 60 grit lines, or the steel is heating too quickly to control). Up from t he 120's come the Gator belts at 100 micron then 60(?) micron. To give an idea of lifetime .... two years ago I bought my first 100 micron gator from pops .... and just last week I put it in the trash. You get the picture ... the 60's are the workhorse and get trashed frequently ... the higher grits last longer and longer.
One final thought - making kitchen knives, my stock is usually 0.7 - 0.9 MAX. I would NOT want to use a grit lower than 60 for the initial grind, as it would take way too much to get out those really deep gouges from, say, 36 grit ... and with that thin stock, there is not a lot of metal to play with .... so I always start at 60.
Also, I recently created a thread about "now I get it ... use belts like they are free" (
https://www.bladeforums.com/threads/use-belts-like-they-are-free-ok-now-i-get-it.1755098/ ) take a look. I stand by that. Dont get me wrong ... they are not free (at least for the hobbyist) .... but the difference between a fresh belt and even a moderately used belt is incredible.