I believe that the scholarship allotments changed a lot when the NCAA limit was reduced from 5 to 4.5 about 20 years ago. I was familiar with the allotment at SMU in Dallas in the late 1970s. They would usually give 5 full scholarships, then talk one good recruit into paying his own way for his freshman year, with the promise that he would get a full scholarship when someone graduated at the end of that year. One or two walk-ons were on the team for practice purposes and in case someone got injured. A precarious roster situation in the eyes of many coaches today, no doubt, but it worked well and it enabled them to do well in recruiting because of the offer of a full scholarship. It was not an uncommon practice at the time among schools in Texas that they competed with.
When the limit became 4.5, everything changed. It would be hard to have the right size roster if you offered 4 full scholarships and one half scholarship. The potential wait for the no-scholarship recruit to get money could scare them off. At 4.5, everyone started dividing scholarships up into various sized pieces. For flexibility, coaches today do not tend to promise exact amounts (e.g. start out at 25%, then I will increase you to 50% the second year, then 75%, etc.). Instead, the standard thing seems to be that, if you do well, your money will increase. That gives the coach flexibility to increase the money slightly, if recruiting is going well and he needs the money for incoming stars, or more substantially, and in either case to some odd fraction of a scholarship.