A staggering number of pages on the World Wide Web are illegible to many viewers. There's text too small to read. There's text hiding other text. There's text overflowing the boxes it was intended to fit in.
Even "professional" web developers often make pages as if they were designing for a piece of paper. The Web is not paper, and that is what makes it so versatile.
A well-coded page will look good (but not necessarily exactly the same) in any browser, on any platform or operating system, no matter what your preferred window size, font-size or screen resolution. Unfortunately, many pages fall apart if anything is very different from the designer's set-up. Many web developers apparently do not understand that you cannot dictate exactly what a viewer's page will look like.
To work well for the most possible viewers, a page must be flexible. The ironic thing about the mess that is the Web is that, by default, an HTML page is flexible. It will adjust itself automatically to the dimensions and font-size of the viewer's browser window. For a page not to work, it must be coded so as to prevent it from working.
The same techniques that prevent pages from working universally are often also responsible for making pages with code so convoluted it looks like rocket science. The simpler the page, the easier it is to find errors and fix them; the easier it is to modify them; the easier it is to add new pages using the same design.
HTML is not rocket science, and with a little instruction, anyone can maintain and add their own pages to a web site. You will not need to go back to your designer every time you need to make a change or add a new page. And if you prefer to have the developer maintain the site, he will be able to do it quickly and therefore more cheaply.