As software developers we all have personal preferences, opinions, and beliefs about how software should be written. Some of us like tabs, others prefer spaces, some like 2 spaces, some like 4 spaces, some use code style formatting tools, some do not.
The problem is, when you have a team of developers working on software together these opinions can cause thrash in a code base and spark fractured debate about how things should be done "the right way". This has a serious impact on code base maintainability, can waste significant amounts of time, can be bad for morale, and does not promote for others to learn different (and potentially better) ways of writing code.
Having a code style guide aims to allow these discussions to happen but to ultimately make a decision as a team (or entire company) on each issue that arises as a conflict of preference. As a code style guide grows and hopefully as tooling to enforce these rules improves, this will reduce friction in PRs and between developers.