It depends on how much it is...and very much on how things work in your relationship.

With us, I do all the financial stuff but I let DH know where we are at, and decisions are made by both of us. TBH he is a bit better at keeping a lid on the spending than me, I tend to drop $10-$20 here & there without asking - but I do let him know after (when the time is right ) - he isn't a spender at all. Anything over $30 is definitely a joint decision, but we both understand that.
He got into online poker a while back & asked me if it was ok to put $50 in an online account - I would have done the same (ask I mean).

But like I said, it's down to both of you undersdtanding where things stand. you might need to let him know what you expect & negotiate some 'rules' (for lack of a better word...)