For example, you want a list of categories in a comma separated list, one after the other, but the default behavior is to add p tags around each category causing them to appear on separate lines.
Two approaches to this:
Use a Plugin to remove the tag
Amend the css so that the tag no longer adds space
for example, where the div is of class commentbody:
.commentbody p{margin-top: 0; padding-top: 0;}
Or
.commentbody p { display: inline; }