This short article will focus on the main three: money, time, and effort.
Basically these are the savings. I'll cover them all, briefly. You will have to supply your own reasons but I'll tell you what I know!
Electronic instruments are cheap. The one thing that some folks ask is this - is 61 keys (the size of most smaller portable keyboards) enough? Yes, it is. If it wasn't, would they even manufacture these things? I, as an instructor, let students know that most music is made within those limits. You don't need 76 or 88 keys. Few pros even use the upper and lower ends, and you ain't a pro, are you? Also, they NEVER need tuning and contain a built-in metronome so you don't need to buy something which easily gets lost.
There is a savings in time. Electronic instruments have many additional and new learning tools. This means less time spent in taking lessons, etc. Also, if you want to learn to play the following: Sax, Clarinet, flute, organ, violin, trumpet, trombone, etc. all you have to do is learn some basics about how those instruments work and the super realistic sounds of an electronic instrument (which you already know how to play!) can make them for you. You don't have to spend the time learning all those instruments.
Finally, keyboards can require less effort. I recall very well my first encounter with the piano. I had already become a professional level organist. Unfortunately, that kind of "always on at full volume" sound doesn’t work on the piano, whose single sound dies away once you make it. Doesn't matter what you do - you gotta produce more notes all the time. I did learn to do this but it wasn't easy. It took quite some time and even now I know that my hands have to keep hitting keys - if I want to continue to hear music, that is! Thus, any electronic instrument which can make other sounds can less work.
Now I know that sales people have sold everyone on "gotta have weighted keys and gotta have 88 of them." I'm here to say that this is simply false data. Who am I to make this claim? I'm Dan Starr and I've been playing all sorts of keyboarded instruments for 40+ years professionally and instructing the same for 25+ years, longer than most clerks have even been alive. I think I know.