Here are a couple of my observations: 1) I take money out of my pocket to complete a job. I want that money coming in as soon as possible and that means billing for it when the work is done. 2) Some customers will quit before the season is over and that means you will NOT get paid for work that was previously completed but has not been billed yet because the billing is 12 equal installments. 3) Customers call asking about the bill saying "you were hardly here in December, January, February, etc, 4) it is impossible that the billing matches the work. Customers like my detailed invoices and statements.
Now understand I do it both ways. For commercial accounts I will bill in 12 equal installments. BUT the contract states work to be done in detail. I charge in the month the work was done for anything not on the contract. If the contract is terminated payment is due in 10 days for all work done at the per item price stipulated in the contract, not the price per month amount.
Residential accounts are per item for maintanence work. For landscaping I will take payments as agreed upon before hand.
I try to be as careful as I can to manage cash flow. But for goodness sakes, get the money as fast as you can after the work is completed. I find the customer forgets about what work was done and the agreements made after the work is completed. I have much more problems with the installment payments. Especially with property management firms that lose the property mid-term and have no way to collect the back money for services completed but not billed for. Just my experiences.