Uniformity amongst controls that are similar helps the user to know what to expect, especially users who are blind or have low vision or cognitive impairments. If different labels are used on controls that have the same function, the user will not be aware that they have already encountered the control elsewhere and may not know what to expect from the control. By ensuring that labels are used consistently throughout a website, such confusion can be avoided.
As well as ensuring that every form control has a <label> element or title attribute, check that the labels are used consistently across a page or across a website. For example, many web pages have a Search form field at the top of the page. There may also be one at the bottom. Both fields should have the same <label>: 'Search'. Furthermore, that label should be consistent across the website.
//At top of the page
<label for="search">Search:</label> <input type="text" name="search" id="search" />
//At bottom of the page (or on another page)
<label for="search">Search:</label> <input type="text" name="search" id="search" />