For starters, I'm going to assume you mean both an XML sitemap and an HTML sitemap, just for safety. And a lot of it really depends on the CMS you're using. For example, WordPress offers a ton of plugins for generating and maintaining XML & HTML sitemaps but a lot of CMSs don't have that functionality baked in and/or they don't have a large enough community that has contributed to building such a plugin. Where I work, we generally try to automate generating and maintaining sitemaps as much as we can but that's not always possible because a lot of CMSs we deal with are dated and fragile, and/or would require an exorbitant amount of time to build an automated sitemap generator. So really it depends on whether or not a plugin already exists for your CMS, how flexible your CMS is and how much time you're willing to dedicate to building this plugin, if it doesn't already exist.
As for best practices, there are really only a few. One best practice that comes to mind is making sure your XML sitemap is well-formed. This is obvious but worth mentioning because I've seen a lot of XML sitemaps that aren't well-formed and there are subsequent indexing issues. This could be just in my own experience but I think a little extra effort is worth preventing any headaches down the road. Another best practice is adding annotations for mobile in your XML sitemap (in the event you have a separate mobile website). You can provide annotations in other ways (i.e. annotations in markup, annotations in detail) but this is the most simplistic approach, especially when dealing with a large website (IMHO).
As for efficiency and SEO, this goes hand in hand with the last paragraph. There are definitely considerations to be taken and I think the biggest one is just making sure your XML sitemap is well maintained. I've dealt with websites that had 1000+ pages and one of the best ways to ensure that as many pages are being indexed as possible is to keep your XML sitemap updated regularly and submit your sitemap to Google Search Console and Bing Webmaster Tools.
