All of these heroes provide some kind of ability (usually their ultimate) that can be very effective in team fight situations. This is great when your team is either lacking team fight ability, or you're trying to stack it across your team.
The only "downside" to these are that generally you want to avoid items like Aghanim's Scepter and Refresher Orb, as they're relatively expensive and don't add much to your damage potential. Occasionally you might be able to look at them once you have plenty of farm