Deleting Beta Character
It will leave an empty slot which is unusable untill next beta which you’d have acces for, or it will be removed if a new stage in the BETA arrives. You cannot use it for a temporary slot…
Been There, Done That & Will do it again…except maybe world completion.
The only reason to delete it is if you believe you will be in the next beta and want to play a different profession from the one you rolled. Otherwise it will either carry through and be playable in the next beta or ANet will wipe it and remove the slot from your select screen before the next round of invites, as they did before this past beta. So you might as well leave it filled so you don’t have to spend time creating a character next time, on the off chance you keep it.
However, you will only be able to use it in the betas. Also apparently any money spent or gained on it goes to a copy of your wallet, not to your live account wallet (according to a dev post). Transmutation charges used in beta do, per some unconfirmed reports, get deducted from your live account.