The real pros are that you gain a prestige CPS multiplier, access to new multiplier bonuses and possibly some achievements. The cons are essentially summed up by you losing almost everything else.
- All achievements earned
- Cookies baked (all-time)
- Golden cookie clicks (all-time)
- Legacy started
- Cookies in bank
- Cookies baked (this game)
- Golden cookie clicks (this game)
- Cookie clicks
- Handmade cookies
- All buildings
- All upgrades
- Session started
- Wrinklers popped
- Elder pledges
- All other stats not yet listed.
- Cookies forfeited by resetting gets cookies baked (this game) added to it
- The number of resets gets incremented
New CPS multipler cookie upgrades based on how many cookies have been forfeited by resetting (14/10/2013):
if (Game.prestige['Heavenly chips']>=1) Game.Unlock('Caramoas');
if (Game.prestige['Heavenly chips']>=2) Game.Unlock('Sagalongs');
if (Game.prestige['Heavenly chips']>=3) Game.Unlock('Shortfoils');
if (Game.prestige['Heavenly chips']>=4) Game.Unlock('Win mints');
if (Game.prestige['Heavenly chips']>=10) Game.Unlock('Fig gluttons');
if (Game.prestige['Heavenly chips']>=100) Game.Unlock('Loreols');
if (Game.prestige['Heavenly chips']>=500) Game.Unlock('Jaffa cakes');
if (Game.prestige['Heavenly chips']>=2000) Game.Unlock('Grease\'s cups');
Any unearned achievements related to the amount of cookies baked (this game) prior to resetting (v.1.036), not cookies in bank:
if (Game.cookiesEarned>=1000000) Game.Win('Sacrifice');
if (Game.cookiesEarned>=1000000000) Game.Win('Oblivion');
if (Game.cookiesEarned>=1000000000000) Game.Win('From scratch');
if (Game.cookiesEarned>=1000000000000000) Game.Win('Nihilism');
Since the reset achievements are cumulative in the sense that gaining a higher tier of the achievement will also gain you the lower tiers, you should wait until your all-time cookies are at least 1 quadrillion in order to get all these achievements in one reset. If you are interested in future-proofing some, you might wait for a quintillion.
//new Game.Achievement('Galactus\' Reprimand','Reset your game with <b>1 quintillion</b> coo- okay no I'm yanking your chain
A CPS multiplier percentage (prestige) based on your cookies forfeited by resetting. Cookies reset only gets cleared on hard resets so your prestige will not decrease, but will be recalculated every time(v.1.036+):
The multiplier is only applied if you purchase the upgrades to unlock it (14/10/2013):
if (Game.Has('Heavenly chip secret')) heavenlyMult+=0.05;
if (Game.Has('Heavenly cookie stand')) heavenlyMult+=0.20;
if (Game.Has('Heavenly bakery')) heavenlyMult+=0.25;
if (Game.Has('Heavenly confectionery')) heavenlyMult+=0.25;
if (Game.Has('Heavenly key')) heavenlyMult+=0.25;
Based on every trillion cookies lost to soft-resetting, a progression is calculated and the resultant value is multiplied by a percentage and used as a multiplier. In v.1.035, the multiplier value of each calculated "Heavenly Chip" (prestige point) was 5%, but, in v.1.036+, it is 2%. Both the progression formula and the value of the prestige CPS multiplier seem likely to change in future updates.
The prestige CPS multiplier is rather low and the geometric progression quite steep. For 1 quadrillion cookies (all-time), you get less than 90% multiplier, and for 1 quintillion, you get about 2800%. For 1000 times the cookies, you only get about 31 times the amount of multiplier.
More problematically is also the issue of having to gain everything again from scratch. The early game was the most fun part of the game so you might consider a reset just to go through it again (but easier due to the effect of the prestige multiplier). Having done so, I can confirm that resetting with a decent all-time and thus a sizable multiplier around 1000% will make it quite easy to get back to where you were before the reset in just a few days time and with each reset, it only gets easier.
To get 2000 Heavenly chips (enough to get the Grease's cups), you would need to have reset away 2,001,000,000,000,000,000 (2.001 quintillion) cookies.
There are also some shadow achievements related to reaching 1 million cookies in a short time without buying the heavenly chip upgrades, but they are not directly related to the prestige system and rather explicitly require you not use it.