why not?

so everytime i were to do a job for someone on the side i should run home and tell the wife "look honey i got $100 today ... what do you want me to do with it?"

what's the harm in having an account where when you do side work or sell something you toss the cash into an account that you use to buy things for the kids or to pay for your hobbies thats not part of the family funds?

i see nothing wrong with it and honestly i've seen plenty of relationships where it would have been beneficial to have a little more seperation of funds. my mom doesnt know what my dad does with all his side earnings and he doesnt dip into the shared accounts for his hobbies or the toys he wants. she obviously knows theres money somewhere when he comes home with a brand new $14k snowmobile that he paid cash for but she doesnt ask how much, where is it or how he gets it.

the last 12 months out of his "private" fund he has purchased:
plane tickets for my mom
his new snowmobile
my sister a new dirtbike
family vacation
new tv's for the house

if you have a CC your partner doesnt know about and you use it to buy things they dont really know about ... how is that any different than having cash stashed to buy things the other doesnt really know about? ones just on credit thats gotta be paid at the end of month with said cash anyways