Karsten, it’s not only the Warp effect, it works like this for any effect.
I test Offset Path, Transform, Rectangle... they all behave like this.

Disabling the Preview doesn’t remove or disable the effect — it just stops updating it while we change the values. It’s 'preview changes'.
It made essential sense in past years, with weaker machines, when calculating an effect in real-time was an effort... makes less today.

I agree that it differs from some other commands, true...
E.g., if we choose Object > Path > Offset Path command and disable Preview there — we won’t see the offset line at all — and that’s because this is basically a filter, creating something new.
At the same time, disabling Preview in the Blend Options dialog with a blend selected won’t remove blending at all. Again, it’s 'preview changes', a comparison with the previous state of the object.

Does it make sense?

Deselecting the Preview checkbox does not display the unchanged illustration. Expected result: As in all other dialogs, the unchanged vectors should be shown when the preview checkbox is unticked.

Illustrator Version 30.1

When I checked going back to version 10, I found that the Effect preview specifications have remained completely unchanged from that time until now.

This is speculation, but in the past, Effect processing was slow, so "Preview OFF" probably existed to avoid real-time rendering.

I speculate that the intended workflow for Effect preview was something like this:

1. Change settings with Preview OFF
2. Turn Preview ON to check the results
3. Turn Preview OFF again to modify numerical values
4. Turn Preview ON to confirm the settings

I believe this kind of repetitive toggle operation was the expected workflow to accommodate the technical limitations of that era.

So what would this Preview option actually do?
1. It should preview only the changes made with the current session of the effect editing
2. It should hide the effect completely (equals to hiding the effect in the stack, removing its influence)

Can you check this one? Does it work aby better than it used to?
There is a general problem about disabling Preview for effects (http://illustrator.uservoice.com/forums/601447/suggestions/38970259), but when I check Warp effects specifically — these do change for me. Do these for you?

@monokano
User Voiceへのご投稿ありがとうございます。
こちらでも再現が確認できましたのでチームに報告させていただきました。エンジニアの方でも認識をしており、修正をお願いしております。

引き続きよろしくお願いします。

*Illustrator 2025 (Beta) (29.9.0 #36)*

When accessing any effect from the Effect menu, unchecking the "Preview" option in the effect dialog box fails to disable the preview. The preview continues to be displayed even when the Preview checkbox is unchecked.

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効果でプレビューのOFFが機能しない

メニューバー「効果」直下の全てで、設定ウィンドウで設定を変更して「プレビュー」をチェックOFFにしても表示が設定変更前に戻りません。チェックOFFの機能が働いていない状態です。

Well, it works, but only to display changes...
It does NOT work, if you want to hide a newly applied shadow.
Is it correct?

Select outline
Select Effect > Distort and Transform > Pucker & Bloat (or any of them except Twist)
Check off or on "preview" in dialog.

Preview does not turn off.

Me too, I check preview and the warp preview doesnt work no matter where I move my slider for the effect

Yes, It's not working in my pc. AI 2020 25v. Win 10.

Even though I have checked the box to show previews for the Warp effect, changing styles does not show a preview of the styles. The only preview that is shown is the very first style that was chosen.

The preview function in the drop shadow panel doesn’t work.

I'm also having this problem with v24.1. No changes preview when adjusting controls (Apply Effects > Warp) or switching between effects. Uninstalled / reinstalled and it's still not working.

Update: Chatted with Adobe ... they had me trash my preferences and restart the application ... problem solved!

I'm still seeing this behaviour in the current shipping version of Illustrator, v24.1. Apply Effects > Warp and Preview doesn't work.

When using the Warp Options dialog, unchecking the Preview box does not show the original object form (doesn't do anything). Then with the preview button unchecked, if I change to a different warp style, the object remains in the previously-selected style until I check the preview box.