Some design choices look impressive in a mockup meeting and cost real calls once the site is live. The rotating image carousel is the clearest example on this list, and the research showing why goes back over a decade, consistently, without anyone finding a counterexample worth citing.
The rotating carousel
A widely cited 2013 study out of Notre Dame found that only about 1% of visitors clicked an auto-forwarding slide, and of those who did, the large majority clicked whatever happened to be the first slide, meaning slides two through five or six were doing essentially nothing. Manually-advanced carousels performed only slightly better. Beyond low engagement, carousels sitting at the top of a page are frequently mistaken for advertising and skipped past entirely, a pattern researchers call banner blindness. One frequently cited test by Adobe for a financial services client found that removing a homepage slider entirely produced a 23% increase in sales. The pattern is old, but nothing since has reversed it: a carousel is a way to hide your second, third and fourth most important messages behind one that almost nobody sees.
The fix isn't complicated: pick the single strongest message and show it, static, without waiting for a rotation nobody watches.
A wall of text with no hierarchy
A page where every paragraph looks the same, same size, same weight, same spacing, forces a visitor to read the whole thing to find what matters. Headings, bold key phrases, and short paragraphs let someone scan first and read second, which is how most people actually approach a page they didn't already decide to read closely.
Autoplay video or audio
Content that starts playing, especially with sound, before a visitor asked for it is one of the fastest ways to make someone leave immediately, particularly on a phone where it's often unexpected and awkward to silence quickly.
Popups that block the page before anyone's read anything
A newsletter signup or a promotional popup that appears before a visitor has seen the page's actual content interrupts the one thing they came to do. If a popup is worth having at all, delaying it until someone has scrolled or spent real time on the page respects the reason they arrived.
Making the phone number hard to find
This deserves its own mention because it's so common and so costly. See click-to-call: why your phone number belongs in the header for the specific fix; the mistake itself is simple: burying the number in a footer or a separate contact page instead of the header, where it needs to be visible on every page without scrolling.
Too many competing calls to action
Five buttons of equal visual weight on one screen, "Call," "Get a Quote," "Learn More," "See Our Work," "Contact," ask a visitor to make a decision before they've decided to act at all. See how to write a call to action that gets calls for how to pick one and make it dominant.
A quick self-check
Load your own homepage and ask: is there a carousel? Does anything autoplay? Is there a popup before any real content has loaded? Is the phone number visible without scrolling? Most of this list can be checked, and often fixed, in under an hour.
Questions
Are carousels ever a good idea?
If the goal is genuinely to showcase multiple photos, a simple static gallery a visitor can browse at their own pace does the same job without hiding messages behind an auto-rotation almost nobody watches.
Is a popup ever acceptable?
A delayed, easily dismissed popup that appears after genuine engagement (real time on the page, meaningful scroll) is far less disruptive than one that blocks the page on arrival.
How do these mistakes relate to page speed?
They compound each other. Autoplay video, unnecessary carousels and heavy popup scripts all add load time on top of hurting usability directly. See core web vitals in plain English for how that's measured.