I know it technically isn't correct, but to me it just looks awkward without it. For example (just reading through a friend's gig review):
'The videos were surprisingly hard hitting, although equally I don’t think Muse will ever get to the Rage Against The Machine level of political activism.'
I think this could be substituted for 'but', which is why I think it works best with a comma.
However, the phrase 'even though' sounds better without one:
'It was incredibly heartwarming to witness even though I wasn’t able to see him myself.'
What are some opinions?
I'm bad with commas (a serial abuser of them), and I'm only really starting to learn English grammar properly!