I think they are necessary. Even though what may seem like a simple mow, blow and go yard, there is always the WHAT IFs that can sometimes get ya. I think it's always best to send them a contract/agreement which shows what services they're receiving for the season along with the costs agreed upon and a general contract that protects you from those WHAT IFs. Example- siding literally touches the ground, you weedeat and rip a hole in it- now you're replacing a section of siding. Our contract states that siding must be 4" min. above the ground or we are not responsible for replacing. More extensive jobs such as a landscape install or hardscape installation, etc. I think they're a definite must. Your warranty statement- such as seed germination/sod, plants getting destroyed by acts of nature, etc. Unforseen issues- such as you start some excavation and then find out there is an underground concrete bunker that no one knew about, etc etc. Proper watering information- if your estimate to them includes a fee for coming and watering, then great. But if you install plants in May and they don't water them ever, come July they want you to replace all the plants you installed because they fried. Nothing worse than getting into a job and finding out your customer thought everything would be perfect no matter happens outside of your control. What the weather does, their pets do, their children do, etc. are just some things that can easily affect your finished product and if you don't have some type of understanding/agreement/contract, there are people out there that will try and hold you responsible to warranty those plants. I think it's always smarter to protect yourself. You can come up with a very simple, easy to read contract that at least offers you some protection.