Do you have any example of words using small katakana like this? I can't come up with any examples.
Generally, small katakana are used to change pronunciations, for example, Sweden (スウェーデン) uses the small e after the u because its a "we" sound, not a "u" sound.
The small Katakana would suggest a longer running sound that's not meant to be, either impulsively or for playful banter.
The ー is actually used to make letters longer, for example, DVD in Japanese Katakana is "ディーブイディー" notice that the "ディ" has a ー next to it to make it longer.