Grids enable you to build solid structure and form into your designs and aren’t just useful for designers or developers – they’re good for the user, too.
After all, the user is there to consume your content and you want to make it as good an experience for them as you can. Having a solid grid system to use in your design, will allow you to do just that, by creating consistency and familiarity in your design.
Using grid system doesn’t mean you should design boxed style of web pages. It gives you responsibility to create a design that has something different and doesn’t restrict you.
In its most basic terms, a grid system is a structure comprising a series of horizontal and vertical lines which intersect and are then used to arrange content. Like all rules, even rules in designing are there to be broken. It is not necessarily always need to stick to grid formation, but it is good to understand it before rule can be broken.
Advantage of using grid system is that they allow you to design in proportions, making balance between all components that you have in your design.