It's always important to keep DX up-to-date if you're a Windows gamer that wants to play the most recent titles. Avoid tomorrow's compatibility issues today.

I recommend downloading the Redistributable version (rather than web installer version) and storing it long-term on your HDD (until the next update at least). Ie if you need to install the latest DX again, you've got the whole thing already on your HDD.

Reinstalling DX always should be one of your first ports of call for when troubleshooting a game.

The Redist version is also great if you run multiple OSes or/and multiple PCs.