Risks of directly modifying the seatle.master page in sharepoint 2013

I am new to SharePoint 2013 . and I have been asked to do a lot of modification to the SharePoint 2013 layout and CSS. So I have created custom CSS inside my document library, but some changes were not achievable without directly modifying the seatle.master page, these modification to the sealt.master which I did include:-

1. Removing some sections.
2. Moving the place of some sections.

 

But lately I have read that we should avoid directly modifying the seatle.master page, and instead we should be modifying the html version of that page. Currently I have almost done all my work on the staging server, and I am planning to start moving my sits to production server so my questions are:-

  1. should I remove all the modification which I made to the seatle.master page (I have copies the original one), and do the modification to the html pages instead.

1. Second question, what are the risks of moving my SharePoint sites to the production , while having the layout changes being implemented directly inside the seatle.master page ?

Can anyone advice please?