项目与项目装载机在剪贴

I'm pretty new to scrapy, I know that items are used to populate scraped data, but I cant understand the difference between items and item loaders. I tried to read some example codes, they used item loaders to store instead of items and I can't understand why. Scrapy documentation wasn't clear enough for me. Can anyone give a simple explanation (better with example) about when item loaders are used and what additional facilities do they provide over items ? I'm pretty new to scrapy, I know that items are