Any disadvantage if I just take the window face off my computer and leave it off?

It will dust up like a mofo.

@jobylie good point

You will also change the air flow.

it looks like it has some glass frontage? if it has then it will probably be ok with regards to dust/air flow. if its not what is it?

@Jilano
Came here to say this, also, you have no protection from physical attacks on your system. This isnt the concern for many, but if you have a pet or someone else who like sticking fingers into fans, it is a valid concern

You will have to find a place to store a medium sized piece of fibre/glass.

You suck at hiding stuff. You've tried to hide your rubber duck but I've detected it! 😁

Sweet DO sticker though

de dust

The airflow in the case is designed to suck in cold air from the front (and top and bottom in most cases) and blast the old.warm air out on the back.

If you open the side, there will be no airflow anymore and you create Hostspots on your components.
Eg HDD and ram. Those parts are only cooled by the airflow created though an closed case.

May sound unreasonable but it can really affect performance and lifetime of you components.

@Rohr my hdds got cooler after i removed my side panel. But my case is shit so that might be the issue.

@jobylie some cases have the option to mount a fan in the front, which will help to cool down HDDs more efficient. A small and slow fan is totally enough from my experience.

I'm - 2 side panels. It's not getting that much dust but it's extremely warm where I live so it helps a lot.