Patches are important not only for game fixes and enhancements, but for game balances and changes in meta. No spectator or player wants to keep playing or watching the same heroes or strategies repeatedly. The experience became stale quickly in the past when all we saw were Sniper, Troll Warlord, Juggernaut, Naga and Axe. When the meta stagnates, it usually means that there is a dire need for a patch.
Valve does not have a fixed schedule for major patch releases, but it seems to fall anytime between 2 to 5 months. However, when they do release a major patch, there is always going to be shifts in the meta. And that also includes the time when they try to release a patch after the Majors or The Internationals.
Sometimes the patches have hero balances, while at other times we have complete revamps of skill sets. We even had the map change drastically to try to balance things out more. Items are also the same as heroes and we have gotten quite a few new items to play with in the last few patches. Hoorah for raindrops and mangoes!
All of this are meant to stimulate the players to improvise their gameplay. When one style becomes overtly dominant it is difficult to attract people's attention and prevent certain teams from dominating the scene completely. There was a patch when we had 5-man death balls, while others had extended gameplay because of “rubber-banding effects” and comeback mechanics. The almighty frozen amphibian tries to make every hero and strategy viable at certain points and sometimes makes drastic changes. Some of which may or may not cause much turmoil for players.
Back to the professional scene. Many teams that would normally do well can be affected instantly by drop in rankings from just a single patch. This is probably why we see an alternation between Western and Chinese Dota teams winning The Internationals. In addition, it is also the reason that keeps everyone interested and excited with Dota 2. Those that are able to adapt to the patch the fastest every time it is released will be able to overtake the competition.
New balances are essentially needed as new heroes such as when the Underlord makes an appearance in the public scene. Once that hero reaches captain mode, all sorts of shenanigans are going to happen. As a result, it will affect everyone from the professional gamers to us public players.
Speaking of new heroes, we already have news of the Monkey King coming this fall. So another hero that will be spammed in public as we climb our solo ranked MMR.
In conclusion, patches are always something we can anticipate, even if it requires reading through a thesis or watching those 2-hour long patch videos in addition to watching people either spamming certain heroes to failure or those who are not aware of why the game was patched.