It is possible to start sending proposals on Upwork without completing your profile, but it is not recommended. Having a complete profile increases your chances of being hired as it showcases your skills, experience, and work history to potential clients. A complete profile also makes it easier for clients to find you when searching for freelancers with specific skills or experience. Additionally, a complete profile can help you stand out from other freelancers who may have incomplete or poorly crafted profiles. Therefore, it is recommended to take the time to fully complete your profile before starting to send proposals on Upwork.