Do you really need a formal contract? Couldn't an email trail documenting the requirements, scope and fees be enough? I am trying to understand the need for for

Do you really need a formal contract? Couldn't an email trail documenting the requirements, scope and fees be enough? I am trying to understand the need for formal contracts as recently I have been taking on more and more consulting projects. My projects are typically high value and short term. I never ask my clients for a formal contract/NDA etc neither do any of my clients. After our phone conversations, I typically summarize the discussion in an email. I prefer to have most of our communication via email after the initial phone discussions. Only safeguard I take is with the new clients. I typically request shorter engagements (< $5K) with $1K-2K as advance payment which all new clients to date have complied. I find that keeping things informal (avoiding or minimizing legalese) keeps my clients comfortable working with me and better relationships. May be it depends on clients, mine tend to be small investment firms (few partners) who most probably care less about legal stuff and more about value they are getting.