Facebook Page Metrics – Difference Between Page Subscriber and Page Likes

You actually deactivate it, and once you do that all your comments, likes, shares, post and everything associated with your profile disappears like it never existed. But your message conversation will still be visible on your friend's inbox just there won't be your profile picture and link to it.

If you reactivate the account in future all your likes, comments etc. will reappear.

Update: If you choose to permanently delete your Facebook profile, the same thing happens plus all your data from facebook servers will be erased permanently, so there's no way you can regain access to your account as well as the data associated with it.

If you want you can download all your data from Facebook before deleting the account. Goto your account settings https://www.facebook.com/settings and click on the link that says "Download a copy of your Facebook data" and download the archive.

Show on Timeline forces the Activity to be shown on the timeline

Allow on Timeline just enables posting of that activity to timeline, it still may or may not end up on your timeline...the power to whether show or not resides with Facebook's feed algorithms

you can always watch over https://facebook.com/{your username}/allactivity to toggle show/allow and also look over what the information apps are logging onto facebook