My understanding is that almost no one drinks 100% Robusta, since it tastes something between burnt tire, wood (not in a good way, in a 'trying to bite raw timber' kind of way) and rubber. However it's very commonly used as, in a positive interpretation, to accentuate the taste of Arabica since it produces more 'crema' on espresso, and in a negative interpretation, as an adulterant to make coffee cheaper to produce.

Here are some people writing about their experience of drinking 100% Robusta: https://old.reddit.com/r/Coffee/comments/6u2ef4/100_robusta_...