If I don't update the plugins for years, what happens? Because I have an e-commerce website and often when I update a plugin I have errors and I lose customers. Is something bad happening if I don't do it? Thank you!
I personally disable all updates; themes/plugins/core, too many times I was burned with erros in the most inconvenient times possible.
Now I do manual updated for each site after I checked in a development environment. after im sure that everything works and I fixed every bug that happened I update the live site.
Now I have far less problems.
The down side is that updated provide the latest and greates (usualy) options, better code, better security and so on.
You can have a plugin that was not updated in a year with a vulnerability that was already patched, in that case you leave yourself open to attacks.
Its up to you to decide what is the best approach to updated.
I disable every update and do regular checks once a week.
The number of calls I have about update problems are far lower now than when the updated were automated.
While I would not recomend automatic updates for the reasons buttered_toast covered. you need to keep in mind that postponing updates means that you develop a "technical debt".
For example lets assume that you do not upgrade for 3 years, but after 3 years you find a plugin you wish top use but it requires an higher version of wordpress. Now you need to check if the rest of your plugins and themes are compatible and test them and then a simple plugin install might become a complex operation of rebuilding or at least test all of the site again.
Usually at the point you need to handle your technical debt you actually don't have the time to properly figure out all the changes in the other plugins and properly test everything which makes it a stressed experiance. It is better to try not to accumulate to much technical debt in the first place and handle upgrades at some reasonable intervals.
The best practice is to keep all plugins up to date. If you aren't able to do that, then you should read the release notes for any updates you're opting out of, to make sure they are not addressing serious issues.
Just recently in the past week, a critical flaw was discovered in WooCommerce (and promptly patched). If you are not updating your site and not staying informed about critical updates, then you are exposing your site and its users to far worse problems than plugin errors.