when managing a Wordpress site it gives me great pleasure to see nothing needs updating. Should I delete the default themes or is it best to leave them there?
By default themes I mean: Twenty Eleven Twenty Twelve Twenty Thirteen
Or should I just update them and keep them there for possible troubleshooting in the future?
It's totally up to you — your choice.
To me, when you have a theme enabled other than "TwentyEleven", "TwentyTwelve" or "TwentyThirteen", why do you need them? Especially when you have limited server space issue, and where every kilobyte is important. (But the server space for a Theme is too minor as to be a non-issue. — said Saildude)
But as you said,
Or should I just update them and keep them there for possible troubleshooting in the future?
Yes, sometimes, we recommend trying any default theme instead of the active one to find a bug. But you know, if you have the cPanel/FTP access, you can upload 'em anytime.
And for Security reasons: I don't think a deactivated theme can be a cause of site hack, especially those are provided by WordPress.org. But you know we are talking about the default themes and default themes only - for the others, I have no opinion.
So, to me, it's totally depends on WHAT YOU WANT.
I keep the default themes in place, and keep them updated.
The WordPress Foundation will keep those themes updated with any security issues, so as long as you keep them updated on your site, I'm not concerned with security problems.
The advantage that you have by keeping them is for testing. When you are troubleshooting an issue, it is very nice to be able to switch temporarily to Twenty Twelve and confirm or eliminate your theme code as the cause of the problem.
If you are not using a theme, it's highly recommended that you delete it. There's no reason to support unused code that could potentially harbor a vulnerability and may be subject to frequent updates. This goes for both unused themes and plugins.
If your WordPress site is subject to a vulnerability and is hacked, it's common for attackers to upload and hide a plethora of infected files in common directories, including your default WordPress theme folders. If you don't have these themes installed, you have effectively made it easier to diagnose and resolve.
Keep at least one and the latest if possible.
The reason for this is if your theme breaks it will revert to the default theme and at least display your content.
But also make sure its always updated.
Also for troubleshooting, sometimes you want to activate the default theme to find problems in your theme.
It is helpful to keep old default themes for testing - however just like with plugins, keeping old themes/plugins will tax your admin and make it slower. For optimal speed and performance, only keep plugins and themes you are actively using.
I can see keep it for testing, but I have always deleted themes I am not using... unless you have built a site on previous theme that uses images and/or [shortcode], I would recommend keeping it until you have fixed all those issues. Reason being, if you move to a new theme and delete the previous theme, it can screw up some pages (if you used shortcode and sometimes even images that may be unique to the previous theme.)
I have found MANY previous themes that I have never deleted from my server that have been infected and thank goodness I never activated that theme, even though the new theme has all the bells and whistles of security.
My answer would have to be, delete them if you have never used them. If you have to revert for testing, take 2 minutes and re-install that theme..... but hey, I could be wrong.
When you are creating new theme with new name you need to activate that from back end and theme will applied to your site . If you delete the defoult theme which one avaiable then when any time you update your wordpress it will automatically switch to its defoult theme . so if there is any issue with your new code you can check that in defoult theme .
