It is a good practice to have utility (helper) CSS classes usually with u- prefix or without any.
However, you never use camel case for class names like in your question, it could be u-padding-top instead but it is also a very good practice to search for a middle way. Try to find the shortest possible name but keep context at the same time. In this specific case for paddings and margins it is common to use today even shorter variant, for example pt10 could be your padding-top: 10 units. The most popular CSS framework Bootstrap 4 already use similar approach.
There is last point to keep in mind. While helpers are good it doesn't mean they should be used everywhere and you should not have next HTML <div class="margin-top-10 font-size-20 color-red"> in any codebase because the main point of HTML is semantics, always use a component styles and override specific elements with utils when needed, i.e.
<div class="panel mt-0"> <!-- reset top margin for 1st panel -->
...
</div>
<div class="panel">
...
</div>
Talking about the semantics in 2017 I would recommend to use custom tags instead of classes for components, i.e. <panel> and not <div class="panel"> and don't forget to add display: block to CSS.
P.S. I still use inline CSS in some cases where I need to make a specific DOM element unique. Later if there is similar styling found in other element util class could be created.
P.S.S. remember that for emails only inline CSS should be used, Today it is usually done with the help of plugins which transform classes into inline CSS.