Nothing against Merlini, but watching solo player's stream and casted tournament is night and day. It's much harder to appreciate good teamfight, check how well the carry is doing or marvel at some of the teamwork from single person's view. I watch a lot of tournaments, but if I watch player's stream, I might as well play the damn game.
People have different tastes, I don't mind watching people play even when I could play myself, it's a bit like watching TV. Obviously if there's a tournament it's better to watch 2 pro teams fighting it out but not always the case. I won't watch a stream for a long time but I'll sometimes check the streams see if they're playing a hero I like and watch one game. Or when a new hero is released, watching dendi or merlini see how they do with the hero(for example first dendi game with skywrath was hilarious cause he apparently hadn't played it in a long time as he was missing his ult by A LOT, he was leading like 200-300unit ahead of the target while skywrath cast point is super low so his ult is more or less point and click).
It's also informative when you don't know as much to see a pro player in first person. Watching a spec or cast game is nice to see stuff on a macro level, teamfights, coordination, map control etc, but to understand how to play, it's a lot better to watch a first person view, see what they look at, how they do thing(like not clicking the shop, putting shit on shortcut, always buying TPs when you can, selling shit, how you bottle crow). It's even better when the guy comment on what's going on, like Merlini or Purge do(but Merlini is a MUCH better player).
Anyway I think it's a sound advice to learn to play, but yeah not necessarily that interesting if you just want to watch the game for fun. There are interesting tidbits I'm sure you can learn but a lot will be too specific to be of any help as a spectator, in this case you're better off watching podcasts and all that shit, which merlini also does I believe on his youtube or something.
