I'm primary but work 0.6.
Pros: When I'm done, I'm done. I don't take marking home and the planning that I do at home is done in the evening taking no longer than 2 hours max. I simply won't spend all my free time working at home anymore, have better priorities.
Spending time with my son, my husband, enjoying my days off.
I have a good job share partner and we work together well, both tidy, both have similar ways of teaching.
Cons: You are still accountable, didn't achieve XYZ results? Tough, doesn't matter if you only teach 2 days, 3 or 4, you are accountable.
Depends how good your school is with communication, will you still go to staff meetings? I miss out on a lot because it is 'mentioned' on a Thursday or Friday.
If you are going to do a job share and you don't get on with them it can be hellish. If you're tidy and they're messy it's a nightmare (or vice versa!), it might be different for Secondary but as a primary job share we obviously both teach literacy and numeracy but divide the other subjects up equally.
If you job share you need to have a good system in place to handover notes to your partner. Email and dropbox are brilliant for this.
I have often thought about returning FT simply because it would make my stress in school less (because I would be fully in charge, responsible, would know what is going on etc). But my stress at home would be huge and no way am I willing to spend less time with my son than I already do. So, for me, PT is better than FT.