The Difference between partial reload and incremental reload is that in partial reload you reload a Qlikview application partially, so suppose you have 100 tables in your qvw but you want to refresh only 10 tables out of those 100 tables then partial reload is what you need.
Incremental reload is when you want to load the data diference for all the 100 tables. so, suppose you reloaded your qvw file yesterday and now today rather than reloading full data you want to load only data which was generated between yesterday and today. then you will do incremental reload.
So, the difference in one line between partial reload and incremental reload is that partial reload if for certain tables and incremental reload is for certain period of data.
Hope this helps.