There are 3 types of LTE scheduling used like Persistent, Semi- Persistent and Dynamic. Every scheduling has its own important based on type of data transmission. I mean sometimes data bur sty in nature or less bur sty.
Depend on your application these scheduling algorithms are used. Normally Dynamic scheduling is used, In which when UE need to send data it send SR(Scheduling request) to Enodeb and then ENodeb allocates resources to UE and inform through DCI(Downlink Control information) over PDCCH channel. If I talk about VoLTE, voice packet size if less but comes at regular interval. so to avoid every time Scheduling Request towards EnodeB, which is a overhead since packets come at regular interval, EnodeB while setting up bearer with qci 1 (which is used for Voice) also perform SPS config towards UE. So In this way Enodeb reduces signalling overhead.
I don't have much clarity about Persistent scheduling.