Well I think 4g is just faster and depending on the resolution of your phone like an ip5 would use more data the ip4 from my experience but 4g network is much faster and more smooth especially on an ip5.. And I know it does uses up alot of data depend on how you use your phone.. I usually use Facebook, Instagram n iMessage sometimes facetime and etc and never use wifi cause I have 6gb on my plan and the most I use in a month is a lol bit over 2gb in a month
Has nothing to do with resolution...if you open a 50mb picture on 4G, the same picture will open with the same amount of data used on LTE. If you watch an HD streamed video on Netflix on 4G, the same amount of data will be used over LTE...the only difference in this is that if you watch videos on higher quality settings, obviously you'll use more data, but this has nothing to do with the kind of network you're on, as you can set video streaming sites (most times) to the quality you prefer. Will these sites automatically upgrade quality on LTE? Yes...but if you watch the same quality video over both types of data network, the same amount of data will be used.
As was said before, because of the faster speeds of LTE, you might find yourself watching more videos because you can load them up faster, and this will obviously use more data...but punch for punch, 3G/4G and LTE do not have a usage difference, only the end user controls that.