Using an airless sprayer to place paint on the wall (using low pressure) will speed up the process because your not having to dip your brush or roller. spray about 3 or 4 sq. ft. and then back brush or roll spreading and evening the paint. Because your using low pressure, mask and cover is at a minimum once you are accustomed to handling the spray gun and the type of surface being painted. Overspray will be larger droplets they tend to fall, than float around.
My husband has been a professional painter over 30 years. He prides himself in his high level of work ethic and customer satisfaction. He stays up to date on techniques and finishes. He gives Very detail and accurate appraisals with contracts. At an alarming rate, as he starts to finish the last day or the day before, the client starts nit picking and being disrespectful towards his work when every day prior to that, they were very pleased, as he request ongoing satisfaction throughout the job. Then they don't to want pay remaining balance, bicker about final cost, or stop payment. He has a crew he has to pay whether the customer does or doesn't honor the contract as well as our own household expenses. Wasted time ,labor, money and effort lost. Now how do we fix this? Remind yourself and clients that a contract is based on honor.