When doing a lot of non-right angle cuts, it makes sense to have one of these Miter saws. It saves an considerable amount of time and frustration while doing your job. Due to the price it may be better to try and rent one for a one-shot job such as building your deck on the house, but if you'll be doing this type of work over and over again to make a full or part-time living I would invest my $$$$.
My Most Used
I have been helping a friend (he's a contractor) build decks over several summers. One of the more popular designs was a herringbone type where the decking is applied to the joists at a 45 degree angle. Every piece of decking has to be cut at the ends with a 45 degree angle and the nail/screw holes all predrilled to prevent the wood splitting. Granted you can set your circular saw to do these cuts but nothing beats having a miter saw setup on a bench. Once the saw is setup at the desired angle, it can repeat the exact same cut time after time without any variation. We did one deck that was 16 feet wide and 35 feet long and we figured that having this saw saved us 2 days on the job. That's just for the decking.
My Other Uses
After completing the decking we had to put up the railings. If you've ever tackled this job you know there's no such thing as a straight cut. Every upright had to be cut on an angle. Then we came to the dreaded stair railings. When cutting the ends for the down slope this saw was invaluable. I've tried cutting these angles with a hand saw and with a circular saw with mixed success. When you're charging people for this work you want to get as close to perfect as you can. The Makita Miter saw is the best I've found for doing this.
One of the features I like the most is the saw's dust catcher that can be attached to these models. It keeps you from making a mess on the floor (if you're working in a house) or on a driveway. People you may be working for (or your mate) don't like messes and this keeps the area neat and clean. The arm is lockable to prevent slipping and there is a full blade guard so that there are no moving parts exposed at any time, making this a very safe saw. The blade brake engages immediately when you let go of the handle button, also another nice safety feature.
As I said before I recommend the Makita Miter saws to anyone who will be doing a lot of angle cuts either at home or on the job. You can rent them at some of the national chair rental centers. It really saves time and frustration. It makes the experience of building your own deck more enjoyable.