Short answer: Do not delete the file manually. Disable Hibernate with an administrator command if you do not use Hibernate or Fast Startup.
What hiberfil.sys does
Windows uses this file to save memory contents when the computer hibernates. It can be several gigabytes because it is linked to installed RAM and power settings.
How to remove it
Open Command Prompt or PowerShell as administrator and run:
powercfg /hibernate off
To restore Hibernate later, run:
powercfg /hibernate on
Tradeoff
You lose Hibernate. Some systems may also change Fast Startup behavior. Sleep still works separately on most PCs.