I pay cash to my T. But I want to answer this from the other side, as I work freelance and sometimes get paid by cheque.

I cash cheques quickly because otherwise I forget, or lose them, and because I think it's poor etiquette to hold onto them for ages. This is especially true with small businesses.

In the case of a therapy client, who is simply an individual person, I think it would be very poor of your T to wait ages to cash it, because you'd have to make sure you didn't spend the money. It's efficient to do it quickly.

But, depending on how a T runs their business, they might find it works best if they cash them at certain points in the week or month.