There are a lot of factors that can adversely affect Sitecore and its performance. Some of them are specific to each individual user, but there are a few common errors that we almost always uncover when running a wellness evaluation.
1. Web Content Expiration. It's incredibly common for users to ignore this particular setting when first installing a Sitecore instance. The recommendation in the Sitecore Installation Manual is seven days, but many users leave the default setting of 'un-configured' in place. The benefit for this setting is mainly to keep Sitecore from reloading static content over and over again in case immediate expiration is in place, or providing stale and outdated content in case this hasn't been set up to expire at all.
2. Remove Link to Master DB. This is a group of settings that again don't come with the default install, but are necessary for the separation of roles, in cases when you have a content authoring production system and a content delivery one (where the live site is). Ignoring the links and leaving them active on the content delivery instance could cause cache clearing event manifestation on that server, which will result in a slowdown for the end users visiting the site when cache clearing happens. Every new request for old resources invokes the resources again from the Sitecore system, which translates to loading times until these resources go into cache again.
3. Nodes with more than 100 items. This is mainly a Sitecore client/content authoring server setting. It is not advertised anywhere by Sitecore (except inside the tuning guide), but developers and mostly content editors might end up creating complex structures inside the Sitecore tree, which might result in more than 100 items per parent node in the tree. This will directly affect performance of the Sitecore client, and the Content Editor will seem incredibly slow. In more extreme cases, it could even affect the performance of the content authoring server itself since the number of items it has can put a strain on the Sitecore API, which can result in performance dropdowns for the content authoring instance.
A CMS is just like any other piece of high-functioning equipment; it requires tune-ups from time to time. Learn more about Hedgehog's Sitecore Wellness Evaluation program, and how our regular scans can help identify problem areas before a crisis occurs.