Besides offering a stock Android experience, LineageOS has features and options which allow ROM users to customize their devices just like they wan, so you get a highly customizable stock Android phone.
As developers themselves claim, it seems that there are some possible reasons for getting the Error 7 while installing the Lineage OS ROM. The Lineage OS you’re trying to flash might not be appropriate for your device. So, make sure that there is no confusion at this chapter.
There are also cases when you’ll see a Trustzone error in the TWRP/CWM before the Error 7. This means that you simply have to upgrade your bootloader before installing the ROM. And yes, you’ll get the very same Status 7 Error when you’re not properly flashing the ROM while migrating from a different ROM.