SVG files have many other curves which are not Bezier curves. I mean lines, circles, ellipses rectangles and maybe some others, too. Bezier curves (also called paths in some programs) can approximate them. A circle converted to a Bezier curve is not nathematically perfect, but it can well be so close the perfect that nobody can see the difference with his eyes. But in graphic programs many useful editing transforms are possible only to Bezier curves. The program can ask at first if such transform is really wanted or it can do the conversion to Bezier curves without asking.
Another good reason to convert non-Bezier SVG curves to Bezier is to make the SVG file usable in incompletely implemented SVG programs which may interpret the SVG file in a wrong way or simply leave something invisible.
Fonts are common cause of harms. Using a font is legal only if one has purchased it and paid what the copyright owner happened to want. To avoid supporting piracy actions SVG files do not include the actual fonts, there's included only the font names and sizes. For example. PDFs and MS Office files carry them, but as neutered in a way that at least Adobe programs refuse to allow any edits which need that font. Edits are allowed if the fonts are also installed where one wants to make the edits. If one opens an SVG file which uses a font which is not installed in the machine the font is replaced by an installed font. The appearance can be totally wrong.
In SVG drawing programs one can convert all fonts to paths (Bezier curves) to make the file universally displayable without font replacements. As a drawback some fine print quality can suffer as well on the screen and as printed because there's not available the rasterization hinting data which is inserted to best fonts to make them look optimally sharp also in small sizes.
Your "convert to Bezier" must mean one or both of the mentioned cases. A good idea is to keep also the version where nothing is converted to Bezier. All texts which are converted to curves are no more editable. And the same for those non-Bezier SVG curves which contain some your program specific editing possibilities or editable effects.