In a rails application, in which situation would you use a partial and when would you use a helper? I find both very similar, since they represent markup fragments.
Partials are the part of view which can have bunch of HTML code along with ruby code. You can also use the partials in controller in render method.
In case of helpers, you can have methods for short html piece of code. You can have some calculations related methods which you want to use in your view file.