A miter saw is definitely a worthwhile asset in any power tool collection. Miter saws are great for the PRO and DIYer for all kinds of cuts and can be used on many different types of materials other than wood.
Rather than focus on the different brands and types (i.e. blade size vs board size, single-bevel vs dual-bevel, sliding vs non-sliding, corded vs cordless), let's talk about the VALUE you can create at the saw.
So how do you do this? Well, different types of saws will definitely help with what you're trying to do, but let's talk more along lines that any motion other than the blade going up and down can be considered opportunities to streamline or improve wasted time at the saw. So, if you had a chance to complete a job faster without sacrificing service or accuracy, why wouldn't you do it? Motions such as measuring, marking, searching for pencils/tape measures, or wrestling with boards could all be considered waste.
Experience lends most to believe there are no shortcuts in construction but wouldn't experience also open your mind to "there's gotta be a better way". Two years ago my partner and I had the same thought when we were reviewing our time at the saw when doing projects. In truth, you can't automate the saw or really the person behind it (well you could, but guys just can't afford those options and would sacrifice mobility). Upon further review, we realized we were doing lots of wasted motion and set out to remove those obstacles.
Some may call this an advertisement, but I'd rather tell you we spent countless hours with a stopwatch and cut a million boards to provide this little insight into how we came up with THE SMART CUT. You'd be just as surprised as we were that those wasted repeated motions in seconds translate to hours saved over the course of a job. See below for examples then ask yourself why wouldn't I do it and what could I do with that extra time?