What are common pitfalls when using Power Query M language for data transformations

What are common pitfalls when using Power Query M language for data transformations?

Before data is ingested into Power BI models, the Power Query M language is put into application to transform the data. This question delves into the user-related problems when dealing with Power Query for example when there are steps that have been done out of order, wrong data types having been assigned, too many manual steps as opposed to dynamic ones and also extra columns being loaded that make the data model heavy. Finding and avoiding such errors helps in better management of data refreshes and data processing in general.